Z80-CPU

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Z80®-CPU Z80A-CPU rechnical Manual Zilog

Price: $7.50 03-0029-01 Copyright© 1977 by Zilog, Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of Zilog. Zilog assumes no responsibility for the use of any circuitry other than circuitry embodied in a Zilog product. No other circuit patent licenses are implied.

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1.0 Introduction

The term "microcomputer" has been used to describe virtually every type of small computing device designed within the last few years. This term has been applied to everything from simple "microprogram­ med" controllers constructed out of TTL MSI up to low end minicomputers with a portion of the CPU constructed out of TTL LSI "bit slices." However, the major impact of the LSI technology within the last few years has been with MOS LSI. With this technology, it is possible to fabricate complete and very power­ ful computer systems with only a few MOS LSI components. The Zilog Z-80 family of components is a significant advancement in the state-of-the art of micro­ computers. These components can be configured with any type of standard semiconductor memory to generate computer systems with an extremely wide range of capabilities. For example, as few as two LSI circuits and three standard TTL MSI packages can be combined to form a simple controller. With additional memory and I/O devices a computer can be constructed with capabilities that only a minicomputer could previously deliver. This wide range of computational power allows standard modules to be constructed by a user that can satisfy the requirements of an extremely wide range of applications. The major reason for MOS LSI domination of the microcomputer market is the low cost of these few LSI components. For example, MOS LSI microcomputers have already replaced TTL logic in such applications as terminal controllers, peripheral device controllers, traffic signal controllers, point of sale terminals, intelligent terminals and test systems. In fact the MOS LSI microcomputer is finding its way into almost every product that now uses electronics and it is even replacing many mechanical systems such as weight scales and automobile controls. The MOS LSI microcomputer market is already well established and new products using them are being developed at an extraordinary rate. The Zilog Z-80 component set has been designed to fit into this market through the following factors: 1. The Z-80 is fully software compatible with the popular 8080A CPU offered from several sources. Existing designs can be easily converted to include the Z-80 as a superior alternative. 2. The Z-80 component set is superior in both software and hardware capabilities to any other micro­ computer system on the market. These capabilities provide the user with significantly lower hardware and software development costs while also allowing him to offer additional features in his system. 3. For increased throughput the Z80A operating at a 4 MHZ clock rate offers the user significant speed advantages over competitive products. 4. A complete product line including full software support with strong emphasis on high level languages and a disk-based development system with advanced real-time debug capabilities is offered to enable the user to easily develop new products. Microcomputer systems are extremely simple to construct using Z-80 components. Any such system consIsts of three parts: L CPU (Central Processing Unit) 2. Memory 3. Interface Circuits to peripheral devices The CPU is the heart of the system. Its function is to obtain instructions from the memory and perform the desired operations. The memory is used to contain instructions and in most cases data that is to be processed. For example, a typical instruction sequence may be to read data from a specific peripheral device, store it in a location in memory; check the parity and write it out to another peripheral device. Note that the Zilog component set includes the CPU and various general purpose 1/0 device controllers, while a wide range of memory deVices may be used from any s.ource. Thus, all required components can be connected together in a very simple manner with virtually no other external logic. The user's effort then becomes primarily one of software development. That is, the user can concentrate on describing his prob­ lem and translating it into a series of instructions that can be loaded into the microcomputer memory. Zilog is dedicated to making this step of software generation as simple as possible. A good example of this is oUr

assembly language in which a simple mnemonic is used to represent every instruction that the CPU can perform. This language is self documenting in such a way that from the mnemonic the user can understand exactly what the instruction is doing without constantly checking back to a complex cross listing.

2.0 Z-80 CPU ARCHITECTURE

A block diagram of the internal architecture of the Z-80 CPU is shown in figure 2.0-1. The diagram shows all of the major elements in the CPU and it should be referred to throughout the following description. CPU AND SYSTEM CONTROL SIGNALS

2.1 CPU REGISTERS

INST. REG CPU CONTROL iii +5V GND <I> 2-80 CPU BLOCK DIAGRAM FIGURE 2.0-1 ALU The Z-80 CPU contains 208 bits of R/W memory that are accessible to the programmer. Figure 2.0-2 illustrates how this memory is configured into eighteen 8-bit registers and four 16-bit registers. All Z-80 registers are implemented using static RAM. The registers include two sets of six general purpose registers that may be used individually as 8-bit registers or in pairs as 16-bit registers. There are also two sets of accumulator and flag registers. Special Purpose Registers 1. Program Counter (PC). The program counter holds the 16-bit address of the current instruction being fetched from memory. The PC is automatically incremented after its contents have been transferred to the address lines. When a program jump occurs the new value is automatically placed in the PC, overriding the incrementer. 2. Stack Pointer (SP). The stack pointer holds the 16-bit address of the current top of a stack located anywhere in external system RAM memory. The external stack memory is organized as a last-in first­ out (LIFO) file. Data can be pushed onto the stack from specific CPU registers or popped off of the stack into specific CPU registers through the execution of PUSH and POP instructions. The data popped from the stack is always the last data pushed onto it. The stack allows simple implementation of multiple level interrupts, unlimited subroutine nesting and simplification of many types of data manipulation.

MAIN ~EG SET ALTERNATE REG SET A A " ,/ ACCUMULATOR FLAGS ACCUMULATOR FLAGS A B H F A' C B' E 0' L H' INTERRUPT I MEMORY VECTOR REFRESH I R INDEX REGISTER IX INDEX REGISTER IY STACK POINTER SP PROGRAM COUNTER PC F·' SPECIAL PURPOSE REGISTERS Z-80 CPU REGISTER CONFIGURATION FIGURE 2.0-2 GENERAL PURPOSE REGISTERS 3. Two Index Registers (IX & IY). The two independent index registers hold a 16-bit base address that is used in indexed addressing modes. In this mode, an index register is used as a base to point to a region in memory from which data is to be stored or retrieved. An additional byte is included in indexed instructions to specify a displacement from this base. This displacement is specified as a two's complement signed integer. This mode of addressing greatly simplifies many types of programs, especially where tables of data are used. 4. Interrupt Page Address Register (I). The Z-80 CPU can be operated in a mode where an indirect call to any memory location can be achieved in response to an interrupt. The I Register is used for this purpose to store the high order 8-bits of the indirect address while the interrupting device provides the lower 8-bits of the address. This feature allows interrupt routines to be dynamically located anywhere in memory with absolute minimal access time to the routine. 5. Memory Refresh Register (R). The Z-80 CPU contains a memory refresh counter to enable dynamic memories to be used with the same ease as static memories. Seven bits of this 8 bit register are auto­ matically incremented after each instruction fetch. The eighth bit will remain as programmed as the result of an LD R, A instruction. The data in the refresh counter is sent out on the lower portion of the address bus along with a refresh control signal while the CPU is decoding and executing the fetched instruction. This mode of refresh is totally transparent to the programmer and does not slow down the CPU operation. The programmer can load the R register for testing purpOSes, but this register is normally not used by the programmer. J)uring refresh, the contents of the I register are placed on the upper 8 bits of the address bus. . Accumulator and Flag Registers The CPU includes two independent 8-bit accumulators and associated 8-bit flag registers. The accumu­ lator !tolds the results of 8-bit arithmetic or logical operations while the flag register indicates specific conditions for 8 or 16-bit operations, such as indicating whether or not the result of an operation is equal to zerO. The programmer selects the accumulator and flag pair that he wishes to work with with a single exchange instruction so that he may easily work with either pair.

There are two matched sets of general purpose registers, each set containing six 8-bit registers that may be used individually as 8-bit registers or as 16-bit register pairs by the programmer. One set is called BC, DE and HL while the complementary set is called BC', DE' and HL'. At anyone time the programmer can select either set of registers to work with through a single exchange command for the entire set. In systems where fast interrupt response is required, one set of general purpose registers and an accumulator/ flag register may be reserved for handling this very fast routine. Only a simple exchange commands need be executed to go between the routines. This greatly reduces interrupt service time by eliminating the require­ ment for saving and retrieving register contents in the external stack during interrupt or subroutine process­ ing. These general purpose registers are used for a wide range of applications by the programmer. They also simplify programming, especially in ROM based systems where little external read/write memory is available.

2.2 ARITHMETIC & LOGIC UNIT (ALU)

The 8-bit arithmetic and logical instructions of the CPU are executed in the ALU. Internally the ALU communicates with the registers and the external data bus on the internal data bus. The type of functions performed by the ALU include: Add Left or right shifts or rotates (arithmetic and logical) Subtract Logical AND Logical OR Logical Exclusive OR Compare Increment Decrement Set bit Reset bit Test bit

2.3 INSTRUCTION REGISTER AND CPU CONTROL

As each instruction is fetched from memory, it is placed in the instruction register and decoded. The control sections performs this function and then generates and supplies all of the control signals necessary to read or write data from or to the registers, control the ALU and provide all required external control signals.

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3.0 Z-BO CPU PIN DESCRIPTION

The Z-80 CPU is packaged in an industry standard 40 pin Dual In-Line Package. The I/O pins are shown in figure 3.0-1 and the function 0 f each is described below. SYSTEM CONTROL CPU MREQ 10RQ RD WR CONTROL INT NMI RESET CPU {BUSRQ BUS CONTROL BUSAK AO-A15 (Address Bus) Ml (Machine Cycle one) MREQ (Memory Request) 'I' +5V GND Z-80 CPU Z-BO PIN CONFIGURATION FIGURE 3.0-1 ADDRESS BUS DATA BUS Tri-state output, active high. AO-A15 constitute a 16-bit address bus. The address bus provides the address for memory (up to 64K bytes) data exchanges and for I/O device data exchanges. I/O addressing uses the 8 lower address bits to allow the user to directly select up to 256 input or 256 output ports. AO is the least significant address bit. During refresh time, the lower 7 bits contain a valid refresh address. Tri-state input/output, active high. DO-D7 constitute an 8-bit bidirectiQnai data bus. The data bus is used for data exchanges with memory and I/O devices. Output, active low. M 1 indicates that the current machine cycle is the OP code fetch cycle of an instruction execution. Note that during execution of 2-byte op-codes, Ml is generated as each op code byte is fetched. These two byte op-codes always begin with CBH, DDH, EDH or FDH. Ml also occurs with 10RQ to indicate an interrupt acknowledge cycle. Tri-state output, active low. The memory request signal indicates that the address bus holds a valid address for a memory read or memory write operation.

(Input/Output Request) RD (Memory Read) WR (Memory Write) RFSH (Refresh) HALT (Halt state) WAIT (Wait) INT (Interrupt Request) NMI (Non Maskable Interrupt) Tri-state output, active low. The 10RQ signal indicates that the lower half of the address bus holds a valid I/O address for a I/O read or write op.eration. An IORQ signal is also generated with an Ml signal when an interrupt is being acknowledged to indicate that an interrupt response vector can be placed on the data bus. Interrupt Acknowledge operations occur during Ml time while I/O operations never occur during Ml time. Tri-state output, active low. RD indicates that the CPU wants to read data from memory or an I/O device. The addressed I/O device or memory should use this signal to gate data onto the CPU data bus. Tri-state output, active low. WR indicates that the CPU data bus holds valid data to be stored in the addressed memory or I/O device. Output, active low. RFSH indicates that the lower 7 bits of the address bus contain a refresh address for dynamic memories and the current MREQ signal should be used to do a refresh read to all dynamic memories. Output, active low. HALT indicates that the CPU has executed a HALT soft­ ware instruction and is awaiting either a non maskable or a maskable inter­ rupt (with the mask enabled) before operation can resume. While halted, the CPU executes NOP's to maintain memory refresh activity. Input, active low. WAIT indicates to the Z-80 CPU that the addressed memory or I/O devices are not ready for a data transfer. The CPU continues to enter wait states for as long as this signal is active. This signal allows memory or I/O devices of any speed to be synchronized to the CPU. Input, active low. The Interrupt Request signal is generated by I/O devices. A request will be honored at the end of the current instruction if the: internal software controlled interrupt enable flip-flop (IFF) is enabled and" if the BUSRQ signal is not active. When the CPU accepts the interrupt, an acknowl­ edge signal (IORQ during M 1 time) is sent out at the beginning of the next instruction cycle. The CPU can respond to an interrupt in three different modes that are described in detail in section 5.4 (CPU Control Instructions). Input, negative edge triggered. The non maskable interrupt request line has a higher priority than INT and is always recognized at the end of the current instruction, independent of the status of the interrupt enable flip-flop. NMI automatically forces the Z-80 CPU to restart to location 0066H. The program counter is automatically saved in the external stack so that the user can return to the program that was interrupted. Note that continuous WAIT cycles can prevent the current instruction from ending, and that a BUSRQ will override aNMI.

(Bus Request) BUSAK (Bus Acknowledge) Input, active low. RESET forces the program counter to zero and initializes the CPU. The CPU initialization includes: 1) Disable the interrupt enable flip-flop 2) Set Register I = OOH 3) Set Register R = OOH 4) Set Interrupt Mode 0 During reset time, the address bus and data bus go to a high impedance state and all control output signals go to the inactive state. Input, active low. The bus request signal is used to request the CPU address bus, data bus and tri-state output control signals to go to a high impedance state so that other devices can control these buses. When BUSRQ is activated, the CPU will set these buses to a high impedance state as soon as the current CPU machine cycle is terminated. Output, active low. Bus acknowledge is used to indicate to the requesting device that the CPU address bus, data bus and tri-state control bus signals have been set to their high impedance state and the external device can now control these signals. Single phase TTL level clock which requires only a 330 ohm pull-up resistor to +5 volts to meet all clock requirements ..

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4.0 CPU TIMING

These include: Memo.ry read o.r write I/O device read o.r write Interrupt ackno.wledge ened by the wait signal which will be fully described in the next sectio.n). The fetch cycle (Ml) is used to. the CPU and memo.ry o.r I/O devices and they may have anywhere fro.m three to. five T cycles (again they graphs describe the timing which o.ccurs within any o.f the basic machine cycles. In sectio.n 7, the exact timing fo.r each instructio.n is specified. TCycle <I> Machine Cycle (o.P Code Fetch) (Memory Read) Instruction Cycle (Memory Write) BASIC CPU TIMING EXAMPLE FIGURE 4.0-0 All CPU timing can be broken do.wn into. a few very simple timing diagrams as sho.wn in figure 4.0-1 4.0-1. 4.0-2. 4.0-3. 4.0-4. 4.0-5. 4.0-6_ 4.0-7. Instructio.n OP co.de fetch (Ml cycle) Memo.ry data read o.r write cycles I/O read o.r write cycles Bus Request/ Ackno.wledge Cycle Interrupt Request/Ackno.wledge Cycle No.n maskable Interrupt Request/ Ackno.wledge Cycle Exit from a HALT instructio.n

5.0 Z-80 CPU INSTRUCTION SET

The Z-80 CPU can execute 158 different instruction types including all 78 of the 8080A CPU. The instructions can be broken down into the following major groups:

• Load and Exchange
• Block Transfer and Search
• Arithmetic and Logical
• Rotate and Shift
• Bit Manipulation (set, reset, test)
• Jump, Call and Return
• Input/Output
• Basic CPU Control

5.1 INTRODUCTION TO INSTRUCTION TYPES

The load instructions move data internally between CPU registers or between CPU registers and exter­ nal memory. All of these instructions must specify a source location from which the data is to be moved and a destination location. The source location is not altered by a load instruction. Examples of load group instructions include moves between any of the general purpose registers such as move the data to Register B from Register C. This group also includes load immediate to any CPU register or to any external memory location. Other types of load instructions allow transfer between CPU registers and memory locations. The exchange instructions can trade the contents of two registers. A unique set of block transfer instructions is provided in the Z-80.With a single instruction a block of memory of any size can be moved to any other location in memory. This set of block moves is extremely valuable when large strings of data must be processed. The Z-80 block search instructions are also valuable for this type of processing. With a single instruction, a block of external memory of any desired length can be searched for any 8-bit character. Once the character is found or the end of the block is reached, the instruction automatically terminates. Both the block transfer and the block search instructions can be interrupted during their execution so as to not occupy the CPU for long periods of time. The arithmetic and logical instructions operate on data stored in the accumulator and other general purpose CPU registers or external memory locations. The results of the operations are placed in the accumulator and the appropriate flags are set according to the result of the operation. An example of an arithmetic operation is adding the accumulator to the contents of an external memory location. The results of the addition are placed in the accumulator. This group also includes 16-bit addition and subtraction between 16-bit CPU registers. The rotate and shift group allows any register or any memory location to be rotated right or left with or without carry either arithmetic or logical. Also, a digit in the accumulator can be rotated right or left with two digits in any memory location. The bit manipulation instructions allow any bit in the accumulator, any general purpose register or any external memory location to be set, reset or tested with a single instruction. For example, the most significant bit of register H can be reset. This group is especially useful in control applications and for controlling software flags in general purpose programming. The jump, call and return instructions are used to transfer between various locations in the user's program. This group uses several different techniques for obtaining the new program counter address from specific external memory locations. A unique type of call is the restart instruction. This instruction actually contains the new address as a part of the 8-bit OP code. This is possible since only 8 separate addresses located in page zero of the external memory may be specified. Program jumps may also be achieved by loading register HL, IX or IY directly into the PC, thus allowing the jump address to be a complex furiCtion of the routine being executed.

The input/output group of instructions in the Z-80 allow for a wide range of transfers between external memory locations or the general purpose CPU registers, and the external I/O devices. In each case, the port number is provided on the lower 8 bits of the address bus during any I/O transaction. One instruction allows this port number to be specified by the second byte of the instruction while other Z-80 instructions allow it to be specified as the content of the C register. One major ad­ vantage of using the C register as a pointer to the I/O device is that it allows different I/O ports to share common software driver routines. This is not possible when the address is part of the OP code if the routines are stored in ROM. Another feature of these input instructions is that they set the flag register automatically so that additional operations are not required to determine the state of the input data (for example its parity). The Z-80 CPU includes single instructions that can move blocks of data (up to 256 bytes) automatically to or from any I/O port directly to any memory location. In conjunction with the dual set of general purpose registers, these instructions provide for fast I/O block transfer rates. The value of this I/O instruction set is demonstrated by the fact that the Z-80 CPU can provide all required floppy disk formatting (i.e., the CPU provides the preamble, address, data and enables the CRC codes) on double density floppy disk drives on an interrupt driven basis. Finally, the basic CPU control instructions allow various options and modes. This group includes instructions such as setting or resetting the interrupt enable flip flop or setting the mode of interrupt response.

5.2 ADDRESSING MODES

Most of the Z-80 instructions operate on data stored in internal CPU registers, external memory or in the I/O ports. Addressing refers to how the address of this data is generated in each instruction. This section gives a brief summary of the types of addressing used in the Z-80 while subsequent sections detail the type of addressing available for each instruction group. Immediate. In this mode of addressing the byte following the OP code in memory contains the actual operand. OP Code } one or 2 bytes Operand Examples of this type of instruction would be to load the accumulator with a constant, where the constant is the byte immediately following the OP code. Immediate Extended. This mode is merely an extension of immediate addressing in that the two bytes following the OP codes are the operand. OP code one or 2 bytes Operand low order Operand high order Examples of this type of instruction would be to load the HL register pair (l6-bit register) with 16 bits (2 bytes) of data:

Modified Page Zero Addressing. The Z-80 has a special single byte CALL instruction to any of 8 locations in page zero of memory. This instruction (which is referred to as a restart) sets the PC to an effective address in page zero. The value of this instruction.is that it allows a single byte to specify a complete 16-bit address where commonly called subroutines are located, thus saving memory space. I OP Code lone byte b7 bO Effective address is (bS b4 b3 000)2 Relative Addressing. Relative addressing uses one byte of data following the OP code to specify a displacement from the existing program to which a program jump can occur. This displacement is a signed two's complement number that is added to the address of the OP code of the following instruction. OP Code } Jump relative (one byte OP code) Operand 8-bit two's complement displacement added to Address (A+2) The value of relative addressing is that it allows jumps to nearby locations while only requiring two bytes of memory space. For most programs, relative jumps are by far the most prevalent type of jump due to the proximity of related program segments. Thus, these instructions can significantly reduce memory space requirements. The signed displacement can range between +127 and -128 from A + 2. This allows for a total displacement of + 129 to -126 from the jump relative OP code address. Another major advantage is that it allows for relocatable code. Extended Addressing. Extended Addressing provides for two bytes (16 bits) of address to be included in the instruction. This data can be an address to which a program can jump or it can be an address where an operand is located. Low Order Address or Low order operand High Order Address or high order operand Extended addressing is required for a program to jump from any location in memory to any other location, or load and store data in any memory location. When extended addressing is used to specify the source or destination address of an operand, the notation (nn) will be used to indicate the content of memory at nn, where nn is the 16-bit address specified in the instruction. This means that the two bytes of address nn are used as a pointer to a memory location. The use of the parentheses always means that the value enclosed within them is used as a pointer to a memory location. For example, (1200) refers to the contents of memory at location 1200. Indexed Addressing. In this type of addressing, the byte of data following the OP code contains a displacement which is added to oneofthe two index registers (the OP code specifies which index register is used) to form a pointer to memory. The contents of the index register are not altered by this operation. OP Code Displacement Operand added to index register to form a pointer to memory.

An example of an indexed instruction would be to load the contents of the memory location (Index Register + Displacement) into the accumulator. The displacement is a signed two's complement number. Indexed addressing greatly simplifies programs using tables of data since the index register can point to the start of any table. Two index registers are provided since very often operations require two or more tables. Indexed addressing also allows for relocatable code. The two index registers in the Z-80 are referred to as IX and IY. To indicate indexed addressing the notation: is used. Here d is the displacement specified after the OP code. The parentheses indicate that this value is used as a pointer to external memory. Register Addressing. Many of the Z-80 OP codes contain bits of information that specify which CPU register is to be used for an operation. An example of register addressing would be to load the data in register B into register C. Implied Addressing. Implied addressing refers to operations where the OP code automatically implies one or more CPU registers as containing the operands. An example is the set of arithmetic operations where the accumulator is always implied to be the destination of the results. Register Indirect Addressing. This type of addressing specifies a 16-bit CPU register pair (such as HL) to be used as a pointer to any location in memory. This type of instruction is very powerful and it is used in a wide range of applications. I OP Code I} one or two bytes An example of this type of instruction would be to load the accumulator with the data in the memory location pointed to by the HL register contents. Indexed addressing is actually a form of register indirect addressing except that a displacement is added with indexed addressing. Register indirect addressing allows for very powerful but simple to implement memory accesses. The block move and search commands in the Z-80 are extensions of this type of addressing where automatic register incrementing, decrementing and comparing has been added. The notation for indicating register indirect addressing is to put parentheses around the name of the register that is to be used as the pointer. For example, the symbol (HL) specifies that the contents of the HL register are to be used as a pointer to a memory location. Often register indirect addressing is used to specify 16-bit operands. In this case, the register contents point to the lower order portion of the operand while the register contents are automatically incremented to obtain the. upper portion of the operand. Bit Addressing. The Z-80 contains a large number of bit set, reset and test instructions. These instructions allow any memory location or CPU register to be specified for a bit operation through one of three previous addressing modes (register, register indirect and indexed) while three bits in the OP code specify which of'the eight bits is to be manipulated. ADDRESSING MODE COMBINATIONS Many instructions include more than one operand (such as arithmetic instructions or loads). In these cases, two types of addressing may be employed. For example, load can Use immediate addressing to specify the source and register indirect or indexed addressing to specify the destination.

5.3 INSTRUCTION OP CODES

This section describes each of the l-80 instructions and provides tables listing the OP codes for every instruction. In each of these tables the OP codes in shaded areas are identical to those offered in the 8080A CPU. Also shown is the assembly language mnemonic that is used for each instruction. All instruction OP codes are listed in hexadecimal notation. Single byte OP codes require two hex characters while double byte OP codes require'four hex characters. The conversion from hex to binary is repeated here for convenience. Hex Binary Decimal Hex Binary Decimal 0 0000 0 8 = 1000 8 0001 = 1 9 1001 9 2 0010 2 A 1010 10 3 0011 3 B 1011 11 4 0100 4 C 1100 = 12 5 = 0101 5 D 1101 13 6 0110 = 6 E 1110 = 14 7 = 0111 = 7 F 1111 15 l-80 instruction mnemonics consist of an OP code and zero, one or two operands. Instructions in which the operand is implied have no operand. Instructions which have only one logical operand or those in which one operand is invariant (such as the Logical OR instruction) are represented by a one operand mnemonic. Instructions which may have two varying operands are represented by two operand mnemonics. LOAD AND EXCHANGE Table 5.3-1 defines the OP code for all of the 8-bit load instructions implemented in the l-80 CPU. Also shown in this table is the type of addressing used for each instruction. The source of the data is found on the top horizontal row while the destination is specified by the left hand column. For example, load register C from register B uses the OP code 48H. In all of the tables the OP code is specified in hexadecimal notation and the 48H (=01001000 binary) code is fetched by the CPU from the external memory during M1 time, decoded and then the register transfer is automatically performed by the CPU. The assembly language mnemonic fot this entire group is LD, followed by the destination followed by the source (LD DEST., SOURCE). Note that several combinations of addressing modes are possible. For example, the source may use register addressing and the destination may be register indirect; such as load the memory location pointed to by register HL with the contents of register D. The OP code for this operation would be 72. The mnemonic for this load instruction would be as follows: LD (HL),D The parentheses around the HL means that the contents of HL are used as a pointer to a memory location. In all l-80 load instruction mnemonics the destination is always listed first, with the source following. The l-80 assembly language has been defined for ease of programming. Every instruction is self documenting and programs written in l-80 language are easy to maintain. Note in table 5.3-1 that some load OP codes that are available in the l-80 use two bytes. This is an efficient method of memory utilization since 8,16,24 or 32 bit instructions ate implemented in the l-80. Thus often utilized instructions stich as arithmetic or logical operations are only 8-bits which results in better memory utilization than is achieved with fixed instruction sizes such as 16-bits. All load instructions using indexed addressing for either the source or destination location actually use three bytes of memory with the third byte being the displacement d. For example a load register E with the operand pointed to by IX with an offset of +8 would be written: LD E, (IX +8)

The instruction sequence for this in memory would be: OP Code A+l 5E Address A ~D} A+2 08 . Displacement operand The two extended addressing instructions are also three byte instructions. For example the instruction to load the accumulator with the operand in memory location6F32H would be written: LD A, (6F 32H) and its instruction sequence would be: A+l 32 low order address Ad<h,d n OP Code A+2 6F high order address Notice that the low order portion of the address is always the first operand. The load immediate instructions for the general purpose 8-bit registers are two·byte instructions. The instruction load register H with the value 36H would be written: LDH,36H and its sequence would be: Address A ~ OP Code A+l ~ Operand Loading a memory location using indexed addressing for the destination and immediate addressing for the source requires four bytes. For example: would appear as: Address A A+l A+2 A+3 LD (IX - 15), 21H DD} OPCode Fl displacement (-15 in signed two's complement) 21 operand to load Notice that with any indexed addressing the displacement alway~ follows directly after the .OP code. Table 5.3·2 specifies the 16-bit load operations. This table is very similar to the previous one. Notice that the extended addressing capability covers all register pairs. Also notice that register indirect operations specifying the stack pointer are the PUSH and POP instructions. The mnemonic for these instructions is "PUSH" and "POP." These differ from other 16~bit loads in that the stack pointer is automatically decre­ mented and incremented as each byte is pushed onto or popped from the stack respectively. For example the instruction:

is a single byte instruction with the OP code of F5H. When this instruction is executed the following sequence is generated: Decrement SP LD{SP), A Decrement SP ill (SP), F Thus the external stack now appears as follows: DESTINATION REG INDIRECT (SP) (SP+l) F A ~ Top of stack EO IMPLIED 1-----It--+--j--+-+--t--t--+--j--+-+--t--t--t--t----j----1 ED

8 BIT LOAD GROUP

'LD' TABLE 5.3-1

The POP instruction is the exact reverse of a PUSH. Notice that all PUSH and POP instructions utilize a 16-bit operand and the high order byte is always pushed first and popped last. That is a: PUSH BC is PUSH B then C PUSH DE is PUSH D then E PUSH HL is PUSH H then.L POP HL is POP L then H The instruction using extended immediate addressing for the source obviously requires 2 bytes of data following the OP code. For example: LD DE,0659H will be: Address A ~1 OP Code A+ 1 59 Low order operand to register E A+2 06 High order operand to register D In all extended immediate or extended addressing modes, the low order byte always appears first after the OP code. Table 5.3-3 lists the 16-bit exchange instructions implemented in the Z-80. OP code 08H allows the programmer to switch between the two pairs of accumulator flag registers while D9H allows the pro­ grammer to switch between the duplicate set of six general purpose registers. These OP codes are only one byte in length to absolutely minimize the time necessary to perform the exchange so that the duplicate banks can be used to effect very fast interrupt response times. BLOCK TRANSFER AND SEARCH Table 5.3-4 lists the extremely powerful block transfer instructions. All of these instructions operate with three registers. HL points to the source location. DE points to the destination location. BC is a byte counter. After the programmer has initialized these three registers, any of these four instructions may be used. The LDI (Load and Increment) instruction moves one byte from the location pointed to by HL to the location pointed to by DE. Register pairs HL and DE are then automatically incremented and are ready to point to the following locations. The byte counter (register pair BC) is also decremented at this time. This instruc­ tion is valuable when blocks of data must be moved but other types of processing are required between each move. The LDIR (Load, increment and repeat) instruction is an extension of the LDI instruction. The same load and increment operation is repeated until the byte counter reaches the count of zero. Thus, this single instruction can move any block of data from one location to any other. Note that since 16-bit registers are used, the size of the block can be up to 64K bytes (I K = 1024) long and it can be moved from any location in memory to any other location. Furthermore the blocks can be overlapping since there are absolutely no constraints on the data that is used in the three register pairs. The LDD and LDDR instructions are very similar to the LDI and LDIR. The only difference is that register pairs HL and DE are decremented after every move so that a block transfer starts from the highest address of the designated block rather than the lowest.

R E G I S T E R EXT. ADDR. PUSH REG AF AF BC DE HL SP IX IV (nn) (SP) NOTE: The Push & Pop Instructions adjust the SP after every execution AF BC, DE MPLI & HL DE REG. (SP) INDIR. SOURCE REGISTER BC DE HL SP

16 BIT LOAD GROUP

'LD' 'PUSH' AND 'POP' TABLE 5.3-2 EXCHANGES 'EX' AND 'EXX' TABLE 5.3-3 IX DO DO n n DO DO IV IMM. EXT. REG. EXT. ADDR. INDIR. nn (nn) (SP)

• •• ,. j
• "',n ED n n ,,' FD n n FD FD n ~~ DO n DO n n n FD n FD n n n DO FD t pOP INSTRUCTIONS

DESTINATION REG. 'NOIR. SOURCE REG. INDIR. (HL) ED AO ED BO (DE) ED ED 'LDl' - Load (DE>-(HL) Inc HL & DE, Dec BC 'LDlR: - Load (DE)_(HL) Inc HL & DE, Dec Be, Repeat until Be = 0 'LOD' - Load (DEI_IHLI Dec HL & DE, Dec Be 'LDOR' - Load (OE)-IHL) Dec HL & DE, Dec Be, Repeat until Be = 0 Reg HL .points to source Reg DE points to destination Reg Be is byte counter BLOCK TRANSFER GROUP TABLE 5.3-4 Table 5.3-5 specifies the OP codes for the four block search instructions. The first, CPI (compare and increment) compares the data in the accumulator, with the contents of the memory location pointed to by register HL. The result of the compare is stored in one of the flag bits (see section 6.0 for a detailed expla­ nation of the flag operations) and the HL register pair is then incremented and the byte counter (register pair BC) is decremented. ! The instruction CPIR is merely an extension of the CPI instruction in which the compare is repeated until either a match is found or the byte counter (register pair BC) becomes zero. Thus, this single instruc­ tion can search the entire memory for any 8-bit character. The CPD (Compare and Decrement) and CPDR (Compare, Decrement and Repeat) are similar instructions, their only difference being that they decrement HLafter every compare so that they search the memory in the opposite direction. (The search is started at the highest location in the memory block). It should be emphasized again that these block transfer and compare instructions are extremely powerful in string manipulation applications. ARITHMETIC AND LOGICAL Table 5.3-6 lists all of the 8·bit arithmetic operations that can be performed with the accumulator, also listed are the increment (INC) and decrement (DEC) instructions. In all of these instructions, except INC and DEC, the specified 8-bit operation is performed between the data in the accumulator and the source data specified in the table. The result of the operation is placed in the accumulator with the excep­ tion of compare (CP) that leaves the accumulator unaffected. All of these operations affect the flag register as a result of the specified operation. (Section 6.0 provides all of the details on how the flags are affected by any instruction type). INC and DEC instructions specify a register or a memory location as both source and destination of the result. When the source operand is addressed using the index registers the displacement must follow directly. With immediate addressing the actual operand will follow directly. For example the instruction: would appear aa: AND07H Address A ~ OP Code A+1~ Operand

REG. INOIR. (HL) ED 'CPI' A1 Inc HL, Dec BC ED 'CPIR', Inc HL, Dec BC B1 repeat until BC = 0 or find match ED 'CPO' Dec H L & BC A9 ED 'CPDR' Dec HL & BC B9 Repeat until BC = 0 or find match HL points to location in memory to be compared with accumulator

contents

TABLE 5.3-5 Assuming that the accumulator contained the value F3H the result of03H would be placed in the accumulator: Acc before operation Operand Result to Acc 1111 0011 = F3H 00000111 = 07H 0000 0011 = 03H The Add instruction (ADD) performs a binary add between the data in the source location and the data in the accumulator. The subtract (SUB) does a binary subtraction. When the add with carry is specified (AD C) or the subtract with carry (SBC), then the carry flag is also added or subtracted respectively. The flags and decimal adjust instruction (DAA) in the Z-80 (fully described in section 6.0) allow arithmetic operations for: multiprecision packed BCD numbers multiprecision signed or unsigned binary numbers multiprecision two's complement signed numbers Other instructions in this group are logical and (AND), logical or (OR), exclusive or (XOR) and compare (CP). There are five general purpose arithmetic instructions that operate on the accumulator or carry flag. These five are listed in table 5.3-7. The decimal adjust instruction can adjust for subtraction as well as add­ ition, thus making BCD arithmetic operations simple. Note that to allow for this operation the flag N is used. This flag is set if the last arithmetic operation was a subtract. The negate accumulator (NEG) instruction forms the two's complement of the number in the accumulator. Finally notice that a reset carry instruction is not included in the Z-80 since this operation can be easily achieved through other instructions such as a logical AND of the accumulator with itself. Table 5.3-8 lists all of the 16-bit arithmetic operations between 16-bit registers. There are five groups of instructions including add with carry and subtract with carry. ADC and SBC affect all of the flags. These two groups simplify address calculation operations or other 16-bit arithmetic operations.

'ADD' ADDwCARRY 'ADC' SUBTRACT 'SUB' SUBw CARRY 'SBC' 'AND' 'XOR' 'OR' COMPARE 'CP' INCREMENT 'INC' DECREMENT 'DEC' SOURCE REG. INDIR. INDEXED

8 BIT ARITHMETIC AND LOGIC

TABLE 5.3-6 Decimal Adjust Acc, 'DAA' Complement Acc, 'CPL' Negate Acc, 'NEG' (2'5 complement} Complement Carry Flag, 'CCF' Set Carry Flag, 'SCF' (HL} (lX+d} GENERAL PURPOSE AF OPERATIONS TABLE 5.3-7 FD d

'ADD' IX DD DD 09 19 IV FD FD 09 19 DESTINATION ADD WITH CARRV AND HL ED ED SET FLAGS 'A DC' 4A 5A SUB WITH CARRV AND HL ED ED SET FLAGS 'SBC' 42 52 INCREMENT 'INC' DECREMENT 'DEC'

16 BIT ARITHMETIC

TABLE 5.3-8 ROTATE AND SHIFT DD FD ED ED 6A 7A ED ED 62 72 IX IV DO DD DO FD FD FD A major capability of the Z-80 is its ability to rotate or shift data in the accumulator, any general pur­ pose register, or any memory location. All of the rotate and shift OP codes are shown in table 5.3-9. Also included in the Z-80 are arithmetic and logical shift operations. These operations are useful in an extremely wide range of applications including integer multiplication and division. Two BCD digit rotate instructions (RRD and RLD) allow a digit in the accumulator to be rotated with the two digits in a memory location pointed to by register pair HL. (See figure 5.3-9). These instructions allow for efficient BCD arithmetic. BIT MANIPULATION The ability to set, reset and test individual bits in a register or memory location is needed in almost every program. These bits may be flags in a general purpose software routine, indications of external con­ trol conditions or data packed into memory locations to make memory utilization more efficient. The Z-80 has the ability to set, reset or test any bit in the accumulator, any general purpose register or any memory location with a single instruction. Table 5.3-10 lists the 240 instructions that are available for this purpose. Register addressing can specify the· accumulator or any general purpose register on which the operation is to be performed. Register indirect and indexed addressing are available to operate on external memory locations. Bit test operations set the zero flag (Z) if the tested bit is a zero. (Refer to section 6.0 for further explanation of flag operation). JUMP, CALL AND RETURN Figure 5.3-11 Iists all of the jump, call and return instructions implemented in the Z-80CPU. Ajump is a branch in a program where the program counter is loaded with the 16-bit value as specified by one of the three available addressing modes (Immediate Extended, Relative or Register Indirect). Notice that the jump group has several different conditions that can be specified to be met before the jump will be made. If these conditions are not met, the program merely continues with the next sequential instruction. The conditions are all dependent on the data in the flag register. (Refer to section 6.0 for details on the flag register). The immediate extended addressing is used to jump to any location in the memory. This in­ struction requires three bytes (two to specify the 16-bit address) with the low order address byte first followed by the high order address byte.

'RLC' CB CB CB. CB CB CB 07 00 01 02 03 04 'RRC' CB CB CB CB CB CB OF DB 09 OA DB DC 'RL' CB CB CB CB CB CB 17 10 11 12 13 14 'RR' CB CB CB CB CB CB 1F 18 19 lA lB lC 'SLA' CB CB CB CB CB CB 27 20 21 22 23 24 'SRA' CB CB CB CB CB CB 2F 2B 29 2A 2B 2C 'SRL' CB CB CB CB CB CB 3F 38 39 3A 3B 3C r 'RLD' 'RRD' L CB CB OD CB CB CB CB CB !HL) !IX +d) (lY+d) CB DO Fo CB CB 06 d d 06 06 CB DO FD CB CB DE d d DE DE oD Fe CB CB CB 16 d d 16 16 CB DD Fe CB CB IE d d IE IE CB DD FD CB CB 26 d d 26 26 CB DD Fo CB CB 2E d d 2E 2E CB DD Fe CB CB 3E d d 3E 3E ED ED ROTATES AND SHIFTS TABLE 5.3-9 Rotate Left Circular ~ 1.----,:1 Ro"" ~ ~ Right Circular ~ ~ Rotate Left Rotate Right ~ rC- ~ Shift ~ ~ ~ Right Arithmetic ~ r.J __ ~ Shift ~ I ' r Right Logical o H 1 (HL) :~~;e Digit For example an unconditional Jump to memory location 3E32H would be: Address A I C3 I OP Code A+ 1 ~ Low order address A+2 ~ High order address The relative jump instruction uses only two bytes, the second byte is a signed two's complement dis­ placement from the existing PC. This displacement can be in the range of + 129 to -126 and is measured from the address of the instruction OP code. Tmee types of register indirect jumps are also included. These instructions are implemented by loading the register pair HL or one of the index registers IX or IY directly into the PC. This capability allows for program jumps to be a function of previous calculations. A call is a special form of a jump where the address of the byte following the call instruction is pushed onto the stack before the jump is made. A return instruction is the reverse of a call because the data on the top of the stack is popped directly into the PC to form a jump address. The call and return instructions allow for simple subroutine and interrupt handling, Two special return instructions have been included in the Z-80 family of components. The return from interrupt instruction (RETI) and the return from non maskable interrupt (RETN) are treated in the CPU as an unconditional return identical to the OP code C9H. The difference is that (RETI) can be used at the end of an interrupt routine and all Z-80 peripheral chips will recognize the execution of this instruction for proper control of nested priority interrupt handling. This instruction coupled with the Z-80 peripheral devices implementation simplifies the normal return from nested interrupt. Without this feature the following software sequence would be necessary to inform the interrupting device that the interrupt routine is completed:

A BIT 0 CB 1 CB 2 CB 3 CB TEST SF 'BIT" 4 CB 5 CB 6 CB 7 CB 0 CB 1 CB 2 CB 3 CB RESET 9F BIT 'RES' 4 CB 5 CB AF 6 CB 7 CB BF 0 CB 1 CB CF 2 CB 3 CB SET DF BIT 'SET" 4 CB 5 CB EF 6 CB 7 CB FF REGISTER ADDRESSING B C D E H L CB CB CB CB CB CB 40 41 42 43 44 45 CB CB CB CB CB CB 4B 49 4A 4B 4C 4D CB CB CB CB CB CB 50 51 52 53 54 55 CB CB CB CB CB CB 5B 59 SA 5B 5C 5D CB CB CB CB CB CB 60 61 62 63 64 65 CB CB CB CB CB CB 6B 69 6A 6B 6C 6D CB CB CB CB CB GB 70 71 72 73 74 75 CB CB CB CB CB CB 7B 79 7A 7B 7C 7D CB CB CB CB CB CB BO B1 B2 B3 B4 85 CB CB C8 CB CB CB

88 B9 8A 8B 8C 8D

TABLE 5.3-10 REG. INDIR. INDEXED IHL) (lX+d) (lY+d) DD FD CB CB CB 46 d d 46 46 DD FD CB CB CB 4E d d 4E 4E DD FD CB CB CB 56 d d 56 56 CB DD FD CB CB 5E d d 5E 5E DD FD CB CB CB 66 d d 66 66 DD FD CB CB CB 6E d d 6E 6E DD FD CB CB CB 76 d d 76 76 CB DD FD CB CB 7E d d 7E 7E DD FD CB CB CB 86 d d 86 86 CB DD FD CB C8 8E d d 8E 8E DD FD CB CB CB 96 d d 96 96 CB DD FD C8 CB 9E d d 9E 9E CB DD FD C8 CB A6 d d A6 A6 CB DD FD CB CB AE d d AE AE DD FD CB CB CB B6 d d B6 B6 DD FD CB CB CB 8E d d BE BE DD FD CB CB CB C6 d d C6 C6 DD FO CB CB CB CE d d CE CE DD FD CB CB CB D6 d d D6 D6 OD FD CB CB CB DE d d DE DE DD FD CB CB CB . E6 d d E6 E6 DO FD CB CB CB EE d d EE EE DD FD CB CB CB F6 d d F6 F6 DD FD CB CB CB FE d d FE FE

LDA,n OUTn,A Enable Interrupt Return prevent interrupt before routine is exited. notify peripheral that service routine is complete This seven byte sequence can be replaced with the one byte EI instruction and the two byte RETI instruction in the l80. TItis is important since interrupt service time often must be minimized. To facilitate program loop control the instruction DJNl e can be used advantageously. This two byte, relative jump instruction decrements the B register and the jump occurs if the B register has not been decre­ mented to zero. The relative displacement is expressed as a signed two's complement number. A simple ex­ ample of its use nlight be: Address N, N+ 1 N + 2 to N+ 9 N + 10, N+ 11 N+ 12 JUMP 'JP' .JUMP 6JR' JUMP 'JP' JUMP 'JP' JUMP 'JP' 'CALL' DECREMENT B, JUMP IF NON ZERO'DJNZ' RETURN 'RET' Instruction LDB, 7 (perform a sequence of instructions) DJNl -8 (Next Instruction) IMMED. nn EXT. RELATIVE PC+e (HL) REG. (IX) INDIR. (IV) IMMED. nn EXT. RELATIVE PC+e REGISTER (SP) INDIR. (SP+l) RETURN FROM REG. (SP) ED (SP+l) 4D INT'RET/' INDIR. RETURN FROM NON MASKABLE REG. INT'RETN' INDIR. ED (SP+l) 45 Comments ; set B register to count of 7 ; loop to be performed 7 times ; to jump from N + 12 to N + 2 CONDITION 28 ;w e-2 e-2 NOTE-CERTAIN FLAGS HAVE MORE THAN ONE PURPOSE. REFER TO SECTION 6_0 FOR DETAILS JUMP, CALL and RETURN GROUP TABLE 5.3-11

I'Table 5.3-12 lists the eight OP codes for the restart instruction. This instruction is a .single byte call to any of the eight addresses listed. The simple mnemonic for these eight calls is also shown. The value of this in­ struction is that fr.equently used routines can be called with this instruction to minimize memory usage. INPUT/OUTPUT C A L L A D o R E S S op CODE 'RSTO' 'RST8' 'RST 16' 'RST 24' 'RST 32' 'RST 40' 'RST48' 'RST56' RESTART GROUP TABLE 5.3-12 The Z·80 has an extensive set of Input and Output instructions as shown in table 5.3-13 and table .5.3-14. The addressing of the input or output device can be either absolute or register indirect, using the C register. Notice that in the register indirect addressing mode data can be transferred between the I/O devices and any of the internal registers. In addition eight block transfer instructions have been implemented. These instructions are similar to the memory block transfers except that they use register pair HL for a pointer to the memory source (output commands) or destination (input commands) while register B is used as a byte counter. Register C holds the address of the port for which the input or output command is desired. Since register:a is eight bits in length, the I/O block transfer command handles up to 256 bytes. In the instructions IN A, n and OUT n, A the I/O device address n appears in the lower half of the add­ ress bus (Ao-A7) while the accumulator content is transferred in the upper half of the address bus. In all reg­ ister indirect input output instructions, including block I/O transfers the co'htent of register C is transferred to the lower half of the address bus (device address) while the content of register B is transferred to the upper half of the address bus.

R E G INPUT'IN' A R E S S I INPUT N DESTINATION G 'INI' - INPUT & Inc HL, DecB 'INIR'-INP, Inc HL, Dec B, REPEAT IF B#O REG; INDIR 'IND'-INPUT & Dec HL, DecB 'INDR'-INPUT, Dec HL, Dec B, REPEAT IF 8#0 B C E H L (HL) SOURCE PORT ADDR ESS ED ED ED ED ED ED ED ED ED AA ED BA BLOCK INPUT COMMANDS INPUT GROUP TABLE 5.3-13 CPU CONTROL GROUP The final table, table 5.3-15 illustrates the six general purpose CPU control instructions. The NOP is a do­ nothing instruction. The HALT instruction suspends CPU operation until a subsequent interrupt is received, while the DI and EI are used to lock out and enable interrupts. The three interrupt mode commands set the CPU into any of the three available interrupt response modes as follows. If mode zero is set the interrupting device can insert any instruction on the data bus and allow the CPU to execute it. Mode 1 is a simplified mode where the CPU automatically executes a restart (RST) to location 0038H so that no external hardware is required. (The old PC content is pushed onto the stack). Mode 2 is the most powerful in that it allows for an indirect call to any location in memory. With this mode the CPU forms a 16-bit memory address where the upper 8-bits are the content of register I and the lower 8-bits are supplied by the interrupting device. This address points to the first of two sequential bytes in a table where the address of the service routine is located. The CPU automatically obtains the starting address and performs a CALL to this address. Address of interrupt { 1-----1 service routine Pointer to Interrupt table. Reg. I is upper address, Peripheral supplies lower address

'OUT' 'OUTI' - OUTPUT Inc HL, Decb 'OTIR' - OUTPUT, Inc HL, Dec B, REPEAT IF B~ 'OUTD' - OUTPUT Dec HL& B 'OTDR' - OUTPUT, Dec HL & B, REPEAT IF B*O SOURCE A IMMED. (n) REG. (C) ED IND. 79 REG. (C) IND. REG. (C) IND. REG. (C) IND. REG. (C) IND. '---y----/ PORT DESTINATION ADDRESS 'NOP' 'HALT' DISABLE INT '(01)' ENABLE INT '(EI)' SETINT MODE 0 'IMO' SET INT MODE 1 'IM1' REGISTER B C 0 ED ED ED 41 49 51 OUTPUT GROUP TABLE 5.3-14 ED 46 8080AMODE E ED ED

56 CALL TO LOCATION 0038 H

H ED INDIRECT CALL USING REGISTER L ED SET INT MODE 2 '1M2' ED 5E I AND 8 BITS FROM INTERRUPTING DEVICE AS A POINTER. MISCELLANEOUS CPU CONTROL TABLE 5.3-15 REG. IND. (HLI ED ED ED AB ED BB BLOCK OUTPUT COMMANDS

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6.0 FLAGS

Each of the two Z-80 CPU Flag registers contains six bits of information which are set or reset by various CPU operations. Four of these bits are testable; that is, they are used as conditions for jump, call or return instructions. For example a jump may be desired only if a specific bit in the flag register is set. The four testable flag bits are: 1) Carry Flag (C) - This flag is the carry from the highest order bit of the accumulator. For example, the carry flag will be set during an add instruction where a carry from the highest bit of the accumulator is generated. This flag is also set if a borrow is generated during a subtraction instruction. The shift and rotate instructions also affect this bit. 2) Zero Flag (Z) - This flag is set if the result of the operation loaded a zero into the accumulator. Other­ wise it is reset. 3) Sign Flag (S) - This flag is intended to be used with signed numbers and it is set if the result of the operation was negative. Since bit 7 (MSB) represents the sign of the number (A negative number has a 1 in bit 7), this flag stores the state of bit 7 in the accumulator. 4) Parity/Overflow Flag (P/V) - This dual purpose flag indicates the parity of the result in the accumulator when logical operations are performed (such as AND A, B) and it represents overflow when signed two's complement arithmetic operations are performed. The Z-80 overflow flag indicates that the two's complement number in the accumulator is in error since it has exceeded the maximum pos­ sible (+ 127) or is less than the minimum possible (-128) number than can be represented in two's complement notation. For example consider adding: +120 = 0111 1000 +105 = 0110 1001 C = a 1110 0001 = -95 (wrong) Overflow has occured Here the result is incorrect. Overflow has occurred and yet there is no carry to indicate an error. For this case the overflow flag would be set. Also consider the addition of two negative numbers: -5 = -16 = C = 11111011 1111 0000 1110 1011 = -21 correct Notice that the answer is correct but the carry is set so that this flag can not be used as an over­ flow indicator. In this case the overflow would not be set. For logical operations (AND, OR, XOR) this flag is set if the parity of the result is even and it is reset if it is odd. There are also two non-testable bits in the nag register. Both of these are used for BCD arithmetic. They are: 1) Half carry (H) - This is the BCD carry or borrow result from the least significant four bits of operation. When using the DAA (Decimal Adjust Instruction) this flag is used to correct the result of a previous packed decimal add or subtract. 2) Subtract Flag (N) - Since the algorithm for correcting BCD operations is different for addition or subtraction, this flag is used to specify what type of instruction was executed last so that the DAA operation will be correct for either addition or subtraction. The Flag register can be accessed by the programmer and its format is as follows: I S I Z I X I H I X Ip/VI N I C I X means flag is indeterminate.

Table 6.0-1 lists how each flag bit is affected by various C~U instructions. In this table a '.' indicates that the instruction does not change the flag, an 'X' means that the flag goes to an indeterminate state, a '0' m~ans that it is reset, a '1' means that it is set and the symbol '~' indicates that it is set or reset according to the previous discussion. Note that any instruction not appearing in this table does not affect any of the flags. Table 6.0-1 includes a few special cases that must be described for clarity. Notice that the block search instruction sets the Z flag if the last compare operation indicated a match between the source and the accumulator data. Also, the parity flag is set if the byte counter (register pair Be) is not equal to zero. This same use of the parity flag is made with the block move instructions. Another special case is during block input or output instructions, here the Z flag is used to indicate the state of register B which is used as a byte counter. Notice that when the I/O block transfer is complete, the zero flag will be reset to a zero (i.e. B=O) while in the case of a block move command the parity flag is reset when the operation is complete. A final case is when the refresh or I register is loaded into the accumulator, the interrupt enable flip flopis loaded into the parity flag so that the complete state of the CPU can be saved at any time.

Instruction CZ f\\ S NH Comments ADD A, s; ADC A,s t t V t o t 8-bit add or add with carry SUB s; SBC A, s, CP s, NEG t t V t t 8-bit subtract, subtract with carry, compare and negate accumulator ANDs 0 t P t 0 } Logical operations ORs; XORs 0 t P t 0 0 And set's different flags INC s e t V t 0 f 8-bit increment DECm e t V t t 8-bit decrement ADDDD,ss t e e e o X 16-bit add ADC HL,ss t t V t o X 16-bit add with carry SBC HL,ss t t V t I X 16-bit subtract with carry RLA;RLCA,RRA,RRCA t e e e 0 0 Rotate accumulator RL m; RLC m; RR m; RRC m t t P t 0 0 Rotate and shift location m SLA m; SRA m; SRL m . RLD,RRD e t P t 0 0 Rotate digit left and right DAA t t P t e t Decimal adjust accumulator CPL e • e e I Complement accumulator SCF I e e e 0 0 Set carry CCF t • e • 0 X Complement carry IN r, (C) e t P t 0 0 Input register indirect INI; IND; OUTI; OUTD e t X X I X } Block input and output INIR; INDR; OTIR; OTDR e I X X I X Z = 0 ifB *' 0 otherwise Z = I LDI,LDD eX t X 0 0 } Block transfer instructions LDIR,LDDR eX o X 0 0 P/V = 1 ifBC *' 0, otherwise P/V = 0 CPI, CPIR, CPD, CPDR • t t ~ I X Block search instructions Z = I if A = (HL), otherwise Z = 0 P/V = I if BC *' 0, otherwise P/V = 0 LDA, I; LD A, R e t FFt 0 0 The content of the interrupt enable flip-flop (IFF) is copied into the P/V flag BITb, s e t xix 0 I The state of bit b oflocation s is copied into the Z flag NEG ~ ~ V ~ I ~ Negate accumulator The following notation is used in this table: Symbol Op~tion C Carry/link flag. C=1 if the operation produced a carry from the MSB of the operand or result. Z Zero flag. Z= 1 if the result of the operation is zero. S Sign flag. S=1 if the MSB of the result is one. PlY Parity or overflow flag. Parity (P) and overflow (V) share the same)lllg. Logical operations affect this flag with the parity of the result while arithmetic operations affect this flag with the overflow of the result. If PlY holds parity, P/V=1 if the result of the operation is even, P/V=O if result is odd. If PlY holds overflow, P/V=l if the result of the operation produced an overflow. H Half-carry flag. H=1 if the add or subtract operation produced a carry into or borrow from into bit 4 of the accumulator. N Add/Subtract flag. N=l if the previous operation was a subtract Hand N flags are used in conjunction with the decimal adjust instruction (DAA) to properly correct the re­ sult into packed nco format following addition or sub~tion using operands with packed BCD format. t The flag is affected according to the result of the operation.

• The flag is unchanged by the operation. o The flag is reset by the operation. 1 The flag is set by the operation. X The flag is a "don't care_" V PlY flag affected according to the overflow result of the operation. P PlY flag affected according to the parity result of the operation. Anyone of the CPU registers A, B, C, D, E, H, L. s Any 8-bit location for all the addressing modes allowed for the particular instruction .• S5 Any 16-bit location for all the addressing modes allowed for that instruction. ii Anyone of the two index registers IX or IY .. R Refresh counter. n 8-bit value in range <0. 255> nn 16-bit value in range <0. 65535> m Any 8-bit location for all the addressing modes allowed for the particular instruction. SUMMARY OF FLAG OPERATION TABLE 6.0-1

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7.0 SUMMARY OF OP CODES AND EXECUTION TIMES

The following section gives a summary of the Z-80 instructions set. The instructions are logically arranged into groups as shown on tables 7.0-1 through 7.0-11. Each table shows the assembly language mnemonic OP code, the actual OP code, the symbolic operation, the content of the flag register following the execu­ tion of each instruction, !..he number of bytes required for e.ach instruction as well as the number of memory cycles and the total number of T states (external clock periods) required for the fetching and execution of each instruction. Care has been taken to make each table self-explanatory without requiring any cross refer­ ence with the test or other tables.

Flags OP-Code No. No. No. Symbolic of ofM orT Mnemonic Operation C ZP/V S N H 76 543 210 Bytes Cycles Cycles +- n .... 01 r no 01 r 110 01 llO r 01 llO r +- d .... LD (HL), n (HL) +- n • • • • • • 00 llO llO 2 3 10 +- n .... 00 llO 110 +- d .... +- n .... 00 llO 110 +- d -> +- n -> ... n -> +- n -> LD (nn), A (nn) ... A • • • • • • 00 llOOIO 3 4 13 ... n -> ... n -> LDA,I A ... I • tIFF t 0 0 11 101 101 2 2 9 I 01 010 III LDA,R A ... R • tIFF t 0 0 11 101 101 2 2 9 01 011 III LD I,A I ... A • • • • • • 11 101 101 2 2 9 01 000 III LDR,A R ... A • • • • • • 11 101 101 2 2 9 01 001 III Notes: r, r' means any of the registers A, B, C, D, E, H, L IFF the content of the interrupt enable flip-flop (IFF) is copied into the P/V flag Flag Notation: • = flag not affected, 0 = flag reset, 1 = flag set, X = flag is unknown, ~ = flag is affected according to the result of the operation. S-BIT LOAD GROUP TABLE 7.0-' Comments r, r' Reg. 000 B 001 C 010 D 011 E 100 H 101 L III A

Flap Oo-Cocle No. No. No. Symbolic zl\\ 01 aIM ofT Mnemonic Operation C S N H 76 543 210 Byl .. Cycles Stales Comments LDdd,nn dd_nn • · · · · . 00 ddO 001 3 3 10 dd Pair -n - 00 Be -n - 01 DE LD IX,nn IX-nn • • · · . . 11 011 101 4 4 14 10 HL 00 100001 11 SP -n ... -n ... LDIY,nn IV-nn 00 100 001 -n ... L-(nn) -n ... - n ... LDdd, (nn) ddH -(nn+l) • · . · . . 11 101 101 4 6 20 ddL _Inn) 01 ddl 011 -n ... -n ... IXL -(nn) 00 101 010 -n --n ... LDIY,(nn) IYH-(nn+l)

• · . • · . 11 111 101 4 6 20 IYL _(nn) 00 101 010 -n ... (nn)-L -n ... -n ... LD (nn),dd (nn+l) -ddH · . . · . . 11 101 101 4 6 20 (nnl-ddL 01 ddOOIl -n ... -n ... LD(nn),IX (nn+l) -IXu
• · . • • • 11 011 101 4 6 20 (nil)-IXL 00 100010 -n --n ... LD(nn),IY (M+l)-IYH · · . · . . II III 101 4 6 20 (nn)-IYL 00 100 010 -n ... LDSP, HL SP-HL · . · . · . 11 III 001 1 I 6 LDSP,IX SP-IX • • • · . . 11 011 101 2 2 10

11 III 001

LDSP,IY SP-IY · . · . · . II 111 101 2 2 10

11 III 001 '1'1 Pair

PUSHqq (SP-2) -q'lL · . • · .. 11 qqO 101 1 3 11 00 BC (SP-I) -qqH 01 DE PUSH IX (SP-2)-IXL • • • • • • 11 011 101 2 4 15 10 HL (SP-I) -IXu 11 100 101 11 AF PUSHIY (SP-2l-IYL · . · . · . 11 III 101 2 4 15 (SP-i)-IYH 11 100 101 POPqq qqH--(SP+l) · . • • • • 11 qqO 001 I 3 10 qqL -(SP) POP IX IXH-(SP+I) · . · . • • 11 011 101 2 4 14 IXL -(SP) 11 100 001 POPIY lYH-(SP+I) • • • • · . 11 111 101 2 4 14 lYL -(SP) 11 100 001 Notes: dd Is any of Ihe repsler pairs BC, DE, HL, SP qq is any ofthuesister pairs AF, BC, DE, HL (PAIR)H' (PAIR)L refer io high order and low order eighl bits of the register pair reopeclively. E.g. BeL =C,AFH=A FJaa Notation: • = I\\ag Dol affected, 0 = I\\ag re .. t, 1 = I\\ag set, X = flag is unknown, * I\\ag i. affected accordill/l 10 the resull of the operation. 16-BIT LOAD GROUP TABLE 7.0.2

No. No. No. Symbolic of ofM ofT Mnemonic Operation (' Z V S N H 76 543 210 Bytes Cycles States Comments EX DE, HL DE··HL • • • • • • II 101 all 1 1 4 EXAF,AF' AF ·.AF' • • • • • • 00 001 000 1 I 4 EXX (~M~) • • • • • • 11 all 001 I I 4 Register bank and auxiliary register bank exchange L -(SP) EX (SP), IX IXH++(SP+ I) • • • • • • 11 all 101 2 6 23 IXL - (SP) 11 100 all EX (SP), IY IYH -(SP+I) • • • • • • 11 III 101 2 6 23 IYL -(SP) II 100 all LDI (DE)- (HL) • • I • a a 11 101 101 2 4 16 Load (HL) into DE -DE+I 10 100 000 . (DE), increment the HL - HL+I pain !ers and decrement the byte BC - BC-I counter (BC) LDIR (DEI - (ilL) • • 0 • () 0 II 101 101 2 5 21 IfBC .. a DE - DE+I 10 110000 2 4 16 IfBC = 0 I HL - IIL+I BC' - BC-I Repeat until BC=O LDD (DE) - (lIL) • • t • 0 0 II 101 101 2 4 16 DE-DE-I 10 101 000 HL - HL·I BC - BC-I LDDR (DE)- (HLl • • () • 0 0 II 101 101 2 5 21 IfBC .. 0 DE-DE-I 10 III 000 2 4 16 IfBC= 0 IfL-HL-1 Be-BC-I Repeat until BC = 0 Q) <D CPI ' A-(HL) • I I I I I II 101 101 2 4 16 HL-HL+I 10 100 001 BC'-BC-I Q) <D CPIR A- (HL) • I I I I t 11 101 101 2 5 21 If BC .. a and A .. (H L) HL-HL+I 10 110 001 2 4 16 IfBC = a or A = (HL) BC-BC·I Repeat until A = lllL) or BC=O Q)<D . CrD A-lHL) • I t I I I II 101 101 HL-HL·I 10 101 001 Be-BC·I Q) ia; (,PDR A-(lfL) • t I t I I II 101 101 HL-HL·I 10 III 001 BC-BC·I Repeat un til A = (lfL) or BC = 0 Notes: <D PIV flag is 0 if the result of BC·I = 0, otherwise P/V = I Q) Z flag IS I if A = (HLl, otherwise Z = O. 2 4 2 5 2 4 Flag Notation: • = nag not affected, 0 = flag reset. I = flag set, X = flag is unknown. I = nag i< affected according to the result of the operation. 21 If BC .. a and A .. (H

16 If BC = a or A = (HL)

EXCHANGE GROUP AND BLOCK TRANSFER AND SEARCH GROUP TABLE 7.0-3

~ Symbolic Mnemonic Operation C Z V S N H ADDA,r A-A+r ~ ~ V ~ 0 t ADDA,n A-A+n ~ ~ V ~ 0 t ADD A, (HL) A~· A+ (HL) ~ t V .t 0 t ADD A, (IX+d) A-A + (IX+d) t t V t 0 t I ADD A, (IY+d) A-A+(IY+d) ~ t V 'ADC A,s A-A+s+CY t ~ V t 0 t SUB s A-A-s t t V t I t SBC A,s A-A-s-CY t t V t I t ANDs A-A A s 0 t P t 0 1 OR s A-A V s 0 t P t 0 0 XORs A-A"s 0 t P t 0 0 CP s A - s t t V t I t INCr r '": r+ I • I V t 0 t INC (HL) (HL) - (HL)+ I • I V t 0 t INC (IX+d) (IX+d) - • t V t 0 I (IX+d)+1 INC (IY+d) (IY+d) - • t V I 0 t (IY+d) + I DECm m+-m-I • I V t I I Op-Code No. of 76 543 210 Bytes 10 [QQQ) r I II [QQQJ 110 2 -n - 10 [QQQJ 110 I 11 011 101 3 10 [QQQ] 110 -d - II III 101 3 10 [QQQ] 110 -d - @Q1J IQIQ] IillII [[QQJ !IIQJ (j]JJ IIill 00 r [J]Q] I 00 110 [J]Q] I II Oil 101 3

00 IIO[IQQ]

. d II III 101 3 00 '\\1011001 - d OJITJ No. No. ofM ofT Cycles States I 4 2 7 2 7 5 19 5 19 I 4 3 II 6 23 6 23 Comments r Reg. 000 B 001 C 010 D Oil E 100 H 101 L III A sisanyofr,n, (HL), (IX+d), (IY +d) as shown f or ADD instruction The indica ted bits replace the 000 in the ADD set abov e. misanyofr,(H L), (IX+d), (IY+d) as shown for INC Same format and states as INC. Replace 100 with III I in OP codc. Notes: The V symbol in the P/V flag column indicates that the P/V flag contains the overflow of the result of the operatior.. Similarly the P symbol indicates parity. V = I means overtlow, V = 0 means not overl1ow. P = I means parity of the result is even, P = 0 means parity of the result is odd. Flag Notation: • = flag not affected, 0 = flag reset, I = tlag set, X = nag is unknown. t = flag is affected according to the result of the operation. 8-BIT ARITHMETIC AND LOGICAL GROUP TABLE 7.0-4

Symbolic ~ Mnemonic Operation C Z V S N H DAA Converts ace. t t P ~ • ~ content into packed BCD following add or subtract with packed BCD operands CPL A+-A • • • • 1 1 NEG A+-O-A ~ t V t 1 t CCF CY +-CY ~ • • • 0 X SCF CY +-1 1 • • • 0 0 IMO Set interrupt • • • • • • mode 0 1M 1 Set interrupt • • • • • • mode 1 1M2 Set interrupt • • • • • • mode 2 Notes: IFF indicates the interrupt enable flip-flop CY indicates the carry flip-flop. Op-Code No. No. of ofM 76 543 210 Bytes Cycles 00 100 111 1 1 00 101 III 1 1 11 101 101 2 2 01 000 100 00 111 111 1 1 00 110 111 1 1 00 000 000 1 1 01 110 110 1 1 11 110011 1 1 11 111 011 1 1 11 101 101 2 2 01 000 110 11 101 101 2 2 01 010 110 11 101 101 2 2 01 011 110 Flag Notation: • = flag not affected, 0 = flag reset, 1 = flag set, X = flag is unknown, t = flag is affected according to the result of the operation. No. ofT States Comments

4 Decimal adjust

4 Complement

(one's complemen t) 8 Negate ace. (two's complement)

4 Complement c

4 Set carry flag

GENERAL PURPOSE ARITHMETIC AND CPU CONTROL GROUPS > TABLE 1.0-5

Flags Op-<:ode Symbolic Mnemonic Operation C Z r" S N H 76 543 210 ADD HL, ss HL-HL+ss ~ • • • 0 X 00 ssl 001 ADCHL, ss HL-HL+ss+CY ~ ~ V ~ 0 X 11 101 101 01 551 010 SBC HL, SS HL-HL- 55 -<:Y ~ ~ V ~ I X 11 101 101 01 ssO 010 ADD IX, pp IX-IX+pp ~ • • • 0 X 11 011 101 00 ppl 001 ADD IY,n IY-IY+rr ~ • • • 0 X II III 101 00 rrl 001 INC 55 55-55+1 • • • • • • 00 550 011 INC IX IX - IX + I • • • • • • II Oil 101 00 100 Oil INC IY IY -IY + I • • • • • • II III 101 00 100 011 DEC ss ss +- ss - 1 • • • • • • 00 551 011 DEC IX IX-lX-I • • • • • • II 011 101 00 101 011 DECIY IY-IY-I • • • • • • 11 III 101 00 101 Oil Notes: ss is any of lhe register pairs BC, DE, HI., SP pp is any of the register pairs BC, DE, IX, SP rr is any of the register pairs BC, DE,IY. SP. No. No. of ofM Bytes Cycles I 3 2 4 2 4 2 4 2 4 1 1 2 2 2 2 I I 2 2 2 2 Flag Notation: • = nag not affected, 0 = tlag reset, I = flag set. X = flag is unknown. ~ = nag is affected according to the result of the operation. 16-BIT ARITHMETIC GROUP TABLE 7.0-6 No. ofT States Comments 11 ss Reg. 00 DC 15 01 DE 10 HL II SP 15 pp Reg. 00 BC 01 DE 10 IX II SP 15 rr Reg. 00 BC 01 DE 10 IY 11 SP

No. Symbolic of Mnemonic Operation C Z V S N H 76 543 210 Bytes RLCA t • • • 0 0 00 000 111 1 A RLA ~ t • • • 0 0 00 010 111 1 A RRCA ~ t • • • 0 0 00 001 111 1 A RRA ~ t • • • 0 0 00 011 111 1 A RLCr t t P t 0 0 11 001 011 2 0010001 r RLC (HL) t t P t 0 0 11 001 011 2 0010001110 RLC (IX+d) ~ t t P t 0 0 11 011 101 4 r. (Ht), (lX+d), (IYi-d) 11 001 011 ~ d -+ 0010001 1 10 RLC (IY+d) t t P t 0 0 11 111 101 4 11 001 OIl ... d -+ 0010001110 RLm L&=E3J t t P t 0 0 10101 mO=l,(HL).(IX+d), (lY+d) RRCm ~La t t P t 0 0 10011 m ~r.(HL), (lX+d), (IY+d) RRm ~ t t P t 0 0 [QTIJ m:=: r, (ilL), (IX+d). (IY+d) SLAm ~o t t P t 0 0 11001 m =:: r, (HL),(lX+d), (IY+d) SRAm ~ t t p t 0 0 [}QI] m == r, (ilL), (IX+d), (IY+d) SRLm o~ t t P t 0 0 [ill] m =r,(HL),(IX+d), (lV+d) RLD A~(HL) • t P t 0 0 11 101 101 2 01 101 111 A~(HL) RRD • t p t 0 0 11 101 101 2 01 100 111 Flag Notation: • =;'ilag not affe~ted, 0 = flag reset, 1 = flag set, X = flag is unknown, t = flag is affected according to the result of the operation. ROTATE AND SHIFT GROUP TABLE 7.0-7 No. No. ofM ofT Cycles States Comments 1 4 Rotate left circular accumulator 1 4 Rotate left accumulator 1 4 Rotate right circular accumulator 1 4 Rotate right accumulator 2 8 Rotate left circular register r 4 15 r R£g. 000 B 6 23 001 C 010 D 011 E 100 H 101 L 6 23 111 A Instruction format a nd states are as shown for RLC,m. To form new OP·code replace [QQQ)of RLC,m with shown code 5 18 Rotate digit left and right between the accumulator and location (HL). 5 18 The content of the upper half of the accumulator is unaffected

Flags Op'("ode /Ilo. No. Symbolic of ofM Mnemonic Operation C Z V S N H 76 543 210 Bytes Cycles BIT b, r Z+-'b • t X X 0 I 11 001 011 2 2 01 b r BIT b, (HL) Z+-(HL)b • t X X 0 I 11 001 011 2 3 01 b 110 BIT b, (IX +d) Z +- (IX+d)b • t X X 0 I 11 011 101 4 5 11 001 011 +- d -+ 01 b 110 BIT b, (IY +d) Z +- (IY+d)b • t X X 0 I 11 III 101 4 5 11 001 011 +- d -+ 01 b 110 SETb, r rb +-1 • • • • • • II 001 011 2 2 ITIJb r SETb, (HL) (HL)b +- I • • • • • 0 11 001 011 2 4 ITIJb 110 11 001 Oil +- d -+ /IIlb 110 SET b, (IY +d) (IY+d)b +- I • • • • • • II III 101 4 6 II 001 011 +- d -+ [TI] b 110 RES b, m ~+-O [!Q] m=r, (HL), (IX+d), (IY+d) Notes: The notation sb indicates bit b (0 to 7) or location s. Flag Notation: • = nag not affected, 0 = nag reset, I = flag set. X = nag is unknown, t = nag is affected according to the result of the operation. BIT SET, RESET AND TEST GROUP TABLE 7.0-8 No. ofT States Comments 8 r Reg. 000 B 12 001 C 010 0 011 E 20 100 H 101 L III A b Bit Tested 20 000 0 001 I 010 2 011 3 100 4 101 5 110 6 111 7 To fonn new Op· code replace IT] of SET b,Ill with @. Flags and time states for SET instruction

No. Symbolic of Mnemonic Operation C Z VS N H 76 543 210 Bytes JP nn PC"'nn • • • • • • 11 000 011 3 JP cc, nn If condition cc • • • • • • 11 cc 010 3 is true PC <-nn, +- n .... otherwise JRC,e IfC = 0, • • • • • • 00 111 000 2 IfC = I, 2 PC ... PC+e JR NC, e IfC = I, • • • • • • 00 110000 2 If C = 0, 2 PC ... PC+e IfZ = I, 2 PC ... PC+e continue -e-2 .... IfZ = 0, 2 pe-PC+e JP(HL) PC-HL • • • • • • II 101 001 I JP (IX) PC-IX • • • • • • II 011 101 2 11 101 001 JP (IV) PC-IV • .. .. • • • II 111 101 2 11 101 001 DJNZ,e B -B·I • • • • • • 00 010 000 2 IfD = 0, - e-2 .... continue IfD '" 0, 2 PC ... PC+e Notes: e represents the extension in the relative addressing mode. e is a signed two's complement number in the range <-126, 129> e-2 in the op-code provides an effective address of pc +e as PC is incremented by 2 prior to the addition of ~ No. ofM Cycles I Flag Notation: .. = flag not affected, 0 = flag reset, 1 = flag set, X = flag is unknown, ~ = flag is affected according to the result of the operation. JUMP GROUP TABLE 7.0-9 No. ofT States Comments cc Condition 10 000 NZnon uro

001 Z zero

010 NCnon carry

011 C carry

100 PO parity odd

101 PE parity even

110 P sign positive

7 If condition not met

12 If condition is met

12 If condition is mel

7 If condition not mt'

12 If condition met

8 IfD = 0

13 IF D '" 0

Flags Op.(:ode No. No. Symbolic of ofM Mnemonic Operation C Z V S N H 76 543 210 Bytes Cycles (SP-2)+-PCL +- n .... PC+-nn +- n .... same as CALLnn PC H <-(SP+l) cc is false continue, 1 3 otheIWise same as RET interrupt 01 001 101 non maskable interrupt 01 000 101 (SP.2)+-PCL PCH+-O PCL .... P Flag Notation: • = flag not affected, 0 = flag reset, 1 = flag set, X = flag is unknown * = flag is affected according to the result of the operation. CAL.L. AND RETURN GROUP TABLE 1.0·10 No. ofT States Comments

10 If cc is false

17 If cc is true

5 If cc is false

11 If cc is true

000 NZ non zero

010 NC non carry

t P .

000 OOH

1. 38H

No. No. Symbolic of ofM Mnemonic Operation C Z V S N H 76 543 210 Bytes Cycles <0- n -+ IN r, (e) r--:-(e) • t P t 0 t II 101 101 2 3 ifr = llO only 01 r 000 the flags will be affected CD INI (HL) +- (C) X t X X I X II 101 101 2 4 B+-B-l 10 100 010 HL+-HL+ 1 INIR (HL) +- (C) X 1 X X 1 X II 101 101 2 5 HL ---HL+ 1 2 4 Repeat until (If B = 0) B=O 'T' '-!.J IND (HL)+- (C) X t X X 1 X 11 101 101 2 4 . B+-B-l 10 101 010 HL---HL-l INDR (HL) +- (C) X 1 X X 1 X II 101 101 2 5 HL+-HL-l 2 4 Repeat until (If B = 0) B=O _n_ 01 r 001 CD OUTI (C) +- (HL) X t X X I X II 101 101 2 4 B+-B-l 10 100011 HL---HL+ 1 OTIR (C) +- (HL) X 1 X X 1 X II 101 101 2 5 HL +-HL + 1 2 4 Repeat until (If B = 0) B=O CD OUTD (C) +-(HL) X t X X 1 X II 101 101 2 4 B +-B - I 10 101 011 HL+-HL-l OTDR (C) ---(HL) X I X X I X II 101 101 2 5 HL+-HL-l 2 4 Repeat until (IfB = 0) B=O Notes: CD If the result of B-1 is zero the Z flag is set, otherwise it is reset· Flag Notation: • = flag not affected, 0 = flag reset, 1 = flag set, X = flag is unknown, t = flag is affected according to the result of the operation. INPUT AND OUTPUT GROUP TABLE 7.0-11 No. ofT States Comments 11 ntoA o -~ Acc to AS - AI5

12 CtoA o-A 7

16 CtoA O -A 7

21 CtoA O - ~

16 CtoA o-A7 . B to AS - Al5

21 Cto AO - A7

12 Cto AO - A7

16 Cto AO - A7

21 Clo Au - A7

16 (' 10 AO - A7 B 10 AS - AI5

8.0 INTERRUPT RESPONSE

The purpose of an interrupt is to allow peripheral devices to suspend CPU operation in an orderly manner and force the CPU to start a peripheral service routine. Usually this service routine is involved with the exchange of data, or status and control information, between the CPU and the peripheral. Once the service routine is completed, the CPU returns to the operation from which it was interrupted. INTERRUPT ENABLE - DISABLE The Z80 CPU has two interrupt inputs, a software maskable interrupt and a non maskable interrupt. The non maskable interrupt (NMI) can not be disabled by the programmer and it will be accepted when­ ever a peripheral device requests it. This interrupt is generaliy reserved.for very important functions that must be serviced whenever they occur, such as an impending power failure. The maskable interrupt (INT) can be selectively enabled or disabled by the programmer. This allows the programmer to disable the inter­ rupt during periods where his program has timing constraints that do not allow it to be interrupted. In the Z80 CPU there is an enable flip flop (called IFF) that is set or reset by the programmer using the Enable Interrupt (EI) and Disable Interrupt (DI) instructions. When the IFF is reset, an interrupt can not be accepted by the CPU. Actually, for purposes that will be subsequently explained, th:ere are two enable flip flops, called IFF I and IFF2. Actually disables interrupts from being accepted. Temporary storage location for IFF I. The state of IFF I is used to actually inhibit interrupts while IFF2 is used as a temporary storage location for IFF 1. The purpose of storing the IFF 1 will be subsequently explained. A reset to the CPU will force both IFF I and IFF 2 to the reset state so that interrupts are disabled. They can then be enabled by an EI instruction at any time by the programmer. When an EI instruction is executed, any pending interrupt request will not be accepted until after the instruction following EI has been executed. This single instruction delay is necessary for cases when the following instruction is a return instruction and interrupts must not be allowed until the return has been completed. The EI instruction sets both IFF 1 and IFF2 to the enable state. When an interrupt is accepted by the CPU, both IFF 1 and IFF2 are automatically reset, inhibiting further interrupts until the programmer wishes to issue a new EI instruc­ tion. Note that for all of the previous cases, IFF 1 and IFF2 are always equal. The purpose of IFF2 is to save the status of IFF} when a non maskable interrupt occurs. When a non maskable interrupt is accepted, IFF} is reset to prevent further interrupts until reenabled by the pro­ grammer. Thus,after a non maskable interrupt has been accepted, maskable interrupts are disabled but the previous state of IFF 1 has been saved so that the complete state of the CPU just prior to the non maskable interrupt can be restored at any time. When a Load Register A with Register I (LD A, I) instruction or a Load Register A with Register R (LD A, R) instruction is executed, the state ofIFF2 is copied into the parity flag where it can be tested or stored. A second method of restoring the status of IFF 1 is thru the execution of a Return From Non Maskable Interrupt (RETN) instruction. Since this instruction indicates that the non maskable interrupt service routine is complete, the contents of IFF2 are now copied back into IFF 1, so that the status of IFF 1 just prior to the acceptance of the non maskable interrupt will be restored automatically.

This mode is the most powerful interrupt response mode. With a single 8 bit byte from the user an indirect call can be made to any memory location. With this mode the programmer maintains a table of 16 bit starting addresses for every interrupt service routine. This table may be located anywhere in memory. When an interrupt is accepted, a 16 bit pointer must be formed to obtain the desired interrupt service routine starting address from the table. The upper 8 bits of this pointer is formed from the contents of the I register. The I register must have been previously loaded with the desired value by the programmer, i.e. LD I, A. Note that a CPU reset clears the I register so that it is initialized to zero. The lower eight bits of the pointer must be supplied by the interrupt­ ing device. Actually, only 7 bits are required from the interrupting device as the least significant bit must be a zero. This is required since the pointer is used to get two adjacent bytes to form a complete 16 bit service routine starting address and the addresses must always start in even locations. Interrupt Service Routine Starting Address Table < low order } high order desired starting address pointed to by: I REG

7 BITS FROM

The first byte in the table is the least significant (low order) portion of the address. The programmer must obviously fill this table in with the desired addresses before any interrupts are to be accep~ed. Note that this table can be changed at any time by the programmer (if it is stored in Read/Write Memory) to allow different peripherals to be serviced by different service routines. Once the interrupting devices supplies the lower portion of the pointer, the CPU automatically pushes the program counter onto the stack, obtains the starting address from the table and does a jump to this address. This mode of response requires 19 clock periods to complete (7 to fetch the lower 8 bits from the interrupting device, 6 to save the program counter, and 6 to obtain the jump address.) , Note that the Z80 peripheral devices all include a daisy chain priority interrupt structure that auto­ matically supplies the programmed vector to the CPU during interrupt acknowledge. Refer to the Z80-PIO; Z80-SIO and Z80-CTC manuals for details.

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9.0 HARDWARE IMPLEMENTATION EXAMPLES

This chapter is intended to serve as a basic introduction to implementing systems with the Z8D-CPU. MINIMUM SYSTEM Figure 9.D·l is a diagram of a very simple Z·8D system. Any Z-8D system must include the following five elements: 1) Five volt power supply 2) Oscillator 3) Memory devices 4) I/O circuits 5) CPU AO-Ag +5V GND ADDRESS IN MREO CE l . 8KBIT RD CE 2 ROM +5V Z80 DATA BUS CPU lORa r AO Ml Al OUTPUT INPUT DATA DATA FIGURE 9.0-1 MINIMUM Z80 COMPUTER SYSTEM Since the Z8D-CPU only requires a single 5 volt supply, most small systems can be implemented using only this single supply. The oscillator can be very simple since the only requirement is that it be a 5 volt square wave. For systems not funning at full speed, a simple RC oscillator can be used. When the CPU is operated near the highest possible frequency, a crystal oscillator is generally required because the system timing will not tolerate the drift or jitter that an RC network will generate. A crystal oscillator can be made from inverters and a few discrete components or monolithic circuits are widely available. The external memory can be any mixture of standard RAM, ROM, or PROM. In this simple example we have shown a single 8K bit ROM (lK bytes) being utilized as the entire memory system. For this example we have assumed that the Z-8D internal register configuration contains sufficient Read/Write storage so that external RAM memory is not required.

Every computer system requires I/O circuits to allow it to interface to the "real world." In this simple example it is assumed that the output is an 8 bit control vector and the input is an 8 bit status word. The input data could be gated onto the data bus using any standard tri-state driver while the output data could be latched with any type of standard TTL latch. For this example we have used a Z80-PIO for the I/O circuit. This single circuit attaches to the data bus as shown and provides the required 16 bits of TTL compatible I/O. (Refer to the Z80-PIO manual for details on the operation of this circuit.) Notice in this example that with only three LSI circuits, a simple oscillator and a single 5 volt power supply, a powerful computer has been implemented. ADDING RAM Most computer systems require some amount of external Read/Write memory for data storage and to implement a "stack." Figure 9.0-2 illustrates how 256 bytes of static memory can be added to the previous example. In this example the memory space is assumed to be organized as follows: MREQ· RD CE, A 10 CE 2 JAO_A g 'K x 8 ROM do-d7 V lK bytes ROM 256 bytes RAM Address OOOOH 03FFH 0400H 04FFH ADDRESS BUS AO-A7 J !!Q.. 00 CE, 256x4 ~ RAM R/W CE 2 dO-d3 V DATA BUS FIGURE 9.()'2 .M!!.Q.!!Q. A,O -.:..: ~ ROM & RAM IMPLEMENTATION EXAMPLE AO-A7

00 CE, ~

R/W CE 2 t--=-=- d4 -d7 IV In this diagram the address space is described in hexidecimal notation. For this example, address bit AlO separates the ROM space from the RAM space so that it can be used for the chip select function. For larger amounts of external ROM or RAM, a simple TTL decoder will be required to form the chip selects. MEMORY SPEED CONTROL For many applications, it may be desirable to use slow memories to reduce costs. The WAIT line on the CPU allows the Z-80 to operate with any speed memory. By referring back to section 4 you will notice that the memory access time requirements are most severe during the Ml cycle instruction fetch. All other memory accesses have an additional one half of a clock cycle to be completed. For this reason it may be desirable in some applications to add one wait state to.the MI cycle so that slower memories can be used. Figure 9.0-3 is an example of a simple circuit that will accomplish this task. This circuit can be changed to add a single wait state to any memory access as shown in Figure 9.0-4.

(1000 to lFFF) WR­ 4Kx8 RAM ARRAY PAGE 0 CE (0000 to OFFF) FIGURE 9.0-5 INTERFACING DYNAMIC RAMS

10.0 SOFTWA~EIMPLEIVIENTATION EXAMPLES

10.1 METHODS OF SOFTWARE IMPLEMENTATION

Several different approaches are possible in developing software for the Z·80 (Figure 10.1). First of all, Assembly Language or PL/Z may be used as the source language. These languages may then be trans· lated into machine language on a commercial time sharing facility using a cross-assembler or cross-compiler or, in the case of assembly language, the translation can be accomplished on a Z-80 Development System using a resident assembler. Finally, the resulting machine code can be debugged either on a time-sharing facility using a Z-80 simulator or on a Z-80 Development System which uses a Z80-CPU directly. SOURCE LANGUAGE ASSEMBLY LANGUAGE PL/Z OR OTHER HIGH LEVEL LANGUAGE TRANSLATION RESIDENT ASSEMBLER CROSS ASSEMBLER CROSS COMPILER FIGURE 10.1 DEBUGGING DEVELOPMENT SYSTEM SIMULATOR In selecting a source language, the primary factors to be considered are Clarity and ease of program­ ming vs. code efficiency. A high level language such as PL/Z with its machine independent constructs is typically better for formulating and maintaining algorithms, but the resulting machine code is usually somewhat less efficient than what can be written directly in assembly language. These tradeoffs can often be balanced by combining PL/Z and assembly language routines, identifying those portions of a task which must be optimized and writing them as assembly language subroutines. Deciding whether to use a resident or cross assembler is a matter of availability and short-term vs. long-term expense. While the initial expenditure for a development system is higher than that for a time­ sharing terminal, the cost of an individual assembly using a resident assembler is negligible while the same operation on a time-sharing system is relatively expensive and in a short time this cost can equal the total cost of a development system. Debugging on a development system vs. a simulator is also a matter of availability and expense com­ bined with operational fidelity and flexibility. As with the assembly process, debugging is less expensive on a development system than on a simulator available through time-sharing. In addition, the fidelity of the operating environment is preserved through real-time'execution on a Z80-CPU and by connecting the I/O and memory components which will actually be used in the production system. The only advantage to the use of a simulator is the range of criteria which may be selected for such debugging procedures as trac­ ing and setting breakpoints. This flexibility exists because a software simulation can achieve any degree of complexity in its interpretation of machine instructions while development system procedures have hard­ ware limitations such as the capacity of the real-time storage module, the number of breakpoint registers and the pin configuration of the CPU. Despite such hardware limitations, debugging on a development system is typically more productive than on a simulator because of the direct interaction that is possible between the programmer and the authentic execution of his program.

10.2 SOFTWARE FEATURES OFFERED BY THE Z80-CPU

The Z-80 instruction set provides the user with a large and flexible repetoire of operations with which to formulate control of the Z80-CPU. The primary, auxiliary and index registers can be used to hold the arguments of arithmetic and logical operations, or to form memory addresses, or as fast-access storage for frequently used data. Information can be moved directly from register to register; from memory to memory; from memory to registers; or from registers to memory. In addition, register contents and register/memory contents can be exchanged without using temporary storage. In particular, the contents of primary and auxilary registers can be completely exchanged by executing only two instructions, EX and EXX. This register exchange procedure can be used to separate the set of working registers between different logical procedures or to expand the set of available registers in a single procedure~ Storage and retrieval of data between pairs of registers and memory can be controlled on a last-in first-out basis through PUSH and POP instructions which utilize a special stack pointer register, SP. This stack register is available both to manipulate data and to automatically store and retrieve addresses for subroutine linkage. When a subroutine is called, for example, the address following the CALL instruction is placed on the top of the push-down stack pointed to by SP. When a subroutine returns to the calling routine, the address on the top of the stack is used to set the program counter for the address of the next instruction. The stack pointer is adjusted automatically to reflect the current "top" stack position during PUSH, POP, CALL and RET instructions. This stack mechanism allows pushdown data stacks and sub­ routine calls to be nested to any practical depth because the stack area can potentially be as large as memory space. The sequence of instruction execution can be controlled by six different flags (carry, zero, sign, parity/overflow, add-subtract, half-carry) which reflect the results of arithmetic, logical, shift and compare instructions. After the execution of an instruction which sets a flag, that flag can be used to control a conditional jump or return instruction. These instructions provide logical control following the manipula­ tion of single bit, eight-bit byte (or) sixtee!l-bit data quantities. A full set of logical operations, including AND, OR, XOR (exclusive - OR), CPL (NOR) and NEG (two's complement) are available for Boolean operations between the accumulator and 1) all other eight-bit registers, 2) memory locations or 3) immediate operands. In addition, a full set of arithmetic and logical shifts in both directions are available which operate on the contents of all eight-bit primary registers or directly on any memory location. The carry flag can be included or simply set by these shift instructions to provide both the testing of shift results and to link register/register or register/memory shift operations.

10.3 EXAMPLES OF USE OF SPECIAL Z80 INSTRUCTIONS

A. Let us assume that a string of data in memory starting at location "DATA" is to be moved into another area of memory starting at location "BUFFER" and that the' string length is 737 bytes. This operation can be accomplished as follows: LD LD LD LDIR HL,DATA DE,BUFFER BC,737 ; START ADDRESS OF DATA STRING ; START ADDRESS OF TARGET BUFFER ; LENGTH OF DATA STRING ; MOVE STRING - TRANSFER MEMORY POINTED TO ; BY HL INTO MEMORY LOCATION POINTED TO BY DE ; INCREMENT HL AND DE, DECREMENT BC ; PROCESS UNTIL BC;: O. 11 bytes are required for this operation and each byte of data is moved in 21 clock cycles.

B. Let's assume that a string in memory starting at location "DATA" is to be moved into another area of memory starting at location "BUFFER" until an ASCII $ character (used as string delimiter) is found. Let's also assume that the maximum string length is 132 characters. The operation can be performed as follows: . LD LD LD LD LOOP:CP JR LDI JP END: HL,DATA DE ,BUFFER BC , 132 A,'$' (HL) Z ,END-$ PE ,LOOP ; STARTING ADDRESS OF DATA STRING ; STARTING ADDRESS OF TARGET BUFFER ; MAXIMUM STRING LENGTH ; STRING DELIMITER CODE ; COMPARE MEMORY CONTENTS WITH DELIMITER ; GO TO END IF CHARACTERS EQUAL ; MOVE CHARACTER (HL) to (DE) ; INCREMENT HL AND DE, DECREMENT BC ; GO TO "LOOP" IF MORE CHARACTERS ; OTHERWISE, FALL THROUGH ; NOTE: P/V FLAG IS USED ; TO INDICATE THAT REGISTER BC WAS ; DECREMENTED TO ZERO. 19 bytes are required for this operation. C. Let us assume that a 16-digit decimal number represented in packed BCD format (two BCD digits/ byte) has to be shifted as shown in the Figure 10.2 in order to mechanize BCD multiplication or division. The operation can be accomplished as follows: LD LD XOR ROTAT:RLD INC DJNZ HL,DATA B,COUNT A HL ROTAT - $ ; ADDRESS OF FIRST BYTE ; SHIFT COUNT ; CLEAR ACCUMULATOR ; ROTATE LEFT LOW ORDER DIGIT IN ACC ; WITH DIGITS IN (HL) ; ADVANCE MEMORY POINTER ; DECREMENT B AND GO TO ROTAT IF ; B IS NOT ZERO, OTHERWISE FALL THROUGH 11 bytes are required for this operation. 4---,,---0 FIGURE 10.2

D. Let us assume that one number is to be subtracted from another and a) that they are both in packed BCD format, b) that they are of equal but varying length, and c) that the result is to be stored in the location of the minuend. The operation can be accomplished as follows: LD LD LD AND SUBDEC:LD SBC DAA LD INC INC DJNZ HL,ARGI DE ,ARG2 B,LENGTH A A, (DE) A, (HL) (HL) , A HL DE SUBDEC - $ ; ADDRESS OF MINUEND ; ADDRESS OF SUBTRAHEND ; LENGTH OF TWO ARGUMENTS ; CLEAR CARRY FLAG ; SUBTRAHEND TO ACC ; SUBTRACT (HL) FROM ACC ; ADJUST RESULT TO DECIMAL CODED VALUE ; STORE RESULT ; ADVANCE MEMORY POINTERS ; DECREMENT B AND GO TO "SUBDEC" IF B ; NOT ZERO, OTHERWISE FALL THROUGH 17 bytes are required for this operation.

10.4 EXAMPLES OF PROGRAMMING TASKS

A. The following program sorts an array of numbers each in the range (0,255) into ascending order using a standard exchange sorting algorithm.

01/22/76 11: 14:37 BUBBLE LISTING PAGE 1 LOC OBJCODE STMT SOURCE STATEMENT 1 * STANDARD EXCHANGE (BUBBLE) SORT ROUTINE *

3 AT ENTRY: HL CONTAINS ADDRESS OF DATA

4 C CONTAINS NUMBER OF ELEMENTS TO BE SORTED

5 (l<C<256)

7 AT EXIT: DATA SORTED IN ASCENDING ORDER

9 USE OF REGISTERS

11 REGISTER CONTENTS

13 A TEMPORARY STORAGE FOR CALCULATIONS

14 B COUNTER FOR DATA ARRAY

15 C LENGTH OF DATA ARRAY

16 D FIRST ELEMENT IN COMPARISON

17 E SECOND ELEMENT IN COMPARISON

18 H FLAG TO INDICATE EXCHANGE

19 L UNUSED

20 IX POINTER INTO DATA ARRAY

21 IY UNUSED

0000 222600 23 SORT: LD (DATA), HL ; SAVE DATA ADDRESS

0003 CB84 24 LOOP: RES FLAG,H ; INITIALIZE EXCHANGE FLAG

0005 41 25 LD B,C ; INITIALIZE LENGTH COUNTER 0006 05 26 DEC B ; ADJUST FOR TESTING

0007 DD2A2600 27 LD IX, (DATA) ; INITIALIZE ARRAY POINTER

OOOB DD7EOO 28 NEXT: LD A, (IX) ; FIRST ELEMENT IN COMPARISON OOOE 57 29 LD D,A ; TEMPORARY STORAGE FOR ELEMENT OOOF DD5E01 30 LD E, (IX+l) ; SECOND ELEMENT IN COMPARISON 0012 93 31 SUB E ; COMPARISON FIRST TO SECOND 0013 3008 32 JR NC, NOEX-$ ; IF FIRST> SECOND, NO JUMP

0015 DD7300 33 LD (IX), E ; EXCHANGE ARRAY ELEMENTS

0018 DD7201 34 LD (IX+1), D

001B CBC4 35 SET FLAG,H ; RECORD EXCHANGE OCCURRED OOlD DD23 36 NOEX: INC IX ; POINT TO NEXT DATA ELEMENT 001F lOEA 37 DJNZ NEXT-$ ; COUNT NUMBER OF COMPARISONS 38 ; REPEAT IF MORE DATA PAIRS

0021 CB44 39 BIT FLAG,H ; DETERMINE IF EXCHANGE OCCURRED

0023 20DE 40 JR NZ,LOOP-$ ; CONTINUE IF DATA UNSORTED

0025 C9 41 RET ; OTHERWISE, EXIT

0026 43 FLAG: EQU 0 ; DESIGNATION OF FLAG BIT 0026 44 DATA: DEFS 2 ; STORAGE FOR DATA ADDRESS

45 END

B. The following program multiplies two unsigned 16 bit integers and leaves the result in the BL register pair. 01/22/76 11:32:36 MULTIPLY LISTING PAGE 1 LOC OBJCODE STMT SOURCE STATEMENT 0000 1 MULT:; UNSIGNED SIXTEEN BIT INTEGER MULTIPLY. 2 ON ENTRANCE: MULTIPLIER IN DE. 3 MULTIPLICAND IN HL. 5 ON EXIT: RESULT IN HL.

7 REGISTER USES:

10 H HIGH ORDER PARTIAL RESULT

11 L LOW ORDER PARTIAL RESULT

12 D HIGH ORDER MULTIPLICAND

13 E LOW ORDER MULTIPLICAND

14 B COUNTER FOR NUMBER OF SHIFTS

15 C HIGH ORDER BITS OF MULTIPLIER

16 A LOW ORDER BITS OF MULTIPLIER

0000 0610 18 LD B,16; NUMBER OF BITS- INITIALIZE 0002 4A 19 LD (:,D; MOVE MULTIPLIER 0003 7B 20 LD A,E;

0004 EB 21 EX DE,HL; MOVE MULTIPLICAND

0005 210000 22 LD HL,O; CLEAR PARTIAL RESULT

0008 CB39 23 MLOOP: SRL C; SHIFT MULTIPLIER RIGHT

OOOA IF 24 RRA LEAST SIGNIFICANT BIT IS 25 IN CARRY. OOOB 3001 26 JR NC, NOADD-$; IF NO CARRY, SKIP THE ADD. OOOD 19 27 ADD HL,DE; ELSE ADD MULTIPLICAND TO 28 PARTIAL RESULT. OOOE EB 29 NOADD: EX DE,HL; SHIFT MULTIPLICAND LEFT OOOF 29 30 ADD HL,HL; BY MULTIPLYING IT BY TWO.

0010 EB 31 EX DE,HL;

0011 IOF5 32 DJNZ MLOOP-$; REPEAT UNTIL NO MORE BITS. 0013 C9 .33 RET;

34 END;

Specified operating range. _65°C to + 150°C -O.3V to +7V l.5W Z80 .. CPU D.C. Characteristics T A = O°C to 70'C. V cc = 5V ± 5'70 unless otherwise specified Symbol Parameter Min. V ILC Clock Input Low Voltage -0.3

• Comment Stresses above those listed under" Absolute Maximum Rating" may quse permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other condition above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Typ. Max. Unit Test Condition 0045 V V 1HC Clock Input High Voltage V cc - .. 6 V cc+·3 V V IL Input Low Voltage -0.3 0.8 V V IH Input High Voltage C.O Vec V VOL Output Low Voltage 004 Y 10L =1.8mA V OH Output High Voltage cA Y 10H = -250pA ICC Power Supply Current 150 rnA ILl Input Leakage Current 10 pA YIN=O to Y ec I LOll Tri-Statc Output Leakage Current in Float 10 pA Y OUT=2A to V Cc ILOL Tri-State Output Leakage Current in Float -10 pA YOUT=OAV ILD Data Bus Leakage Current in Input Mode ±IO pA o <YIN <Vee Z80A·CPU D.C. Characteristics Symbol Parameter Min. Typ. Max. Unit Test Condition VIl.(, Clock Inpnt Low Voltage -0.3 0.45 Y VII 1(' ('lock Input lligh Voltage Vee -_6 V cc+_3 V V 11_ Input Low Voltage -0.3 O.H V Viii Input Iligh Voltage ~.O V~.: V VOL Olltput Luw Voltage OA V IOL=I.SmA V OII Output lIigh VUltage 2.4 V 1011 = -")OpA ICC Power Supply Cur rent 90 200 mA 1\\.1 Input Leakage Cllfrent 10 pA VIN=O tLl Vcc II ()II Tn-SIJte Output Leakage Current in FhKJt 10 pA VOllT=cAto Vcc 11<1I Tri-State Output Leakage l'urrent rn Float -10 /1A VOUT=OAV III> Data Ilu, Leakage Current in Input Mude ±IO pA O<Y IN ';;Vcc Note: For ZBO-CPU a!l AC and DC characteristics remain the same for the military grade parts except Icc. Icc = 200 rnA Capacitance T A = 25°C, f = 1 MHz, unmeasured pins returned to ground Symbol Parameter , Max. Unit C<j> Clock Capacitance 35 pF C IN Input Capacitance 5 pF C OUT Output Capacitance 10 pF Z80·CPU

Ordering Information

S - Standard SY ± S% 0 to 70 C E - Extended SY ±S% -,40° to 85°C M - Military sV ±\\O%-'SSO to \\2SoC Capacitance T A = 2S°e, f = I MHz. unmcasured pins returncd to ground Symbol Parameter Max. ("(IJ C[th.:k ('ap:J(ltaJl(l' 35 C"" IIlPll( CarJ(lI~II1\\"'l' eOl'l Ou tpu t C JP~Ii..:1 talll'~ 10 Z80A-CPU Unit pl- pI' pF S - Standard 5V ±5% 0° to 70°C

A.C. Characteristics Z80-CPU T A = oOe to 70o e, Vee = +5V ± 5%, Unless Otherwise Noted. Signal Symbol Parameter Min tc Clock Periuc.l .4 <I> tw«I>H) Clock Pulse Width. Clock High 180 twt<l>l) Clock Pulse Width. Clock Low 180 II", r Clock Rise :.II1d F<.I1l Time tD(AD) Address Output Delay tF(AD) Delay to Float A O_15 t:u:m Address Stable Prior to MREO (Memury Cycle) III laei Address Stable Prior to 10RO. RD or WR (I/O Cycle) 121 lea Address Stable from RIJ, WR, IORQ or MREQ 131 leaf Address Stable From RD or WR During Flout 141

• tD(D) Data Output Delay tF(D) De,"y to Float During Write Cycle tS<I>(D) Data Setup Time to Rising Edge of Clock During M I Cycle 50 DO_7 ts1i" (0) Data Setup Time to Falling Edge or Clut.:k During M2 to M5 60 Idem Data Stable Prior to WR (Memory Cycle) 15 tdci Data Stable Prior to WR (I/O Cycle) 161 tcdf Data Stable From WR 171 tH Any Hold Time for Setup Time 0 tDl1i" (MR) MREO Delay From Falling Edge of Clock, MREO low IDH<I> (MR) MREO Delay From Rising Edge of Clock, MREO High MREO tDH1i"(MR) MREO Delay From Falling Edge of Clock. MRE'jHigh Iw (MRl) Pulse Width. MREO low 181 Iw(MRH) Pulse Width, MREO High . 191 tDl<l> (IR) 10RO Delay From Rising Edge of Clock, 10RO low IORO tDL1i" (IR) 10RO Delay From Falling Edge of Clock, IORO low tDH<I> (IR) 10RO Delay From Rising Edge of Clock, 10RO High tDH1i"(IR) IORO Delay From Falling Edge of Clock, 10RO High tDl<l> (RD) RD Delay From Rising Edge of Clock, RD low Ri5 tDl1i" (RD) RD Delay From Falling Edge of Clock, RD low tDH<I> (RD) RD Delay From Rising Edge of Clock, RD High tDH<i>(RD) RD Delay From Falling Edge of Clock, RD High IDl<l> (WR) WR Delay From Rising Edge of Clock, WR low WR tDl1i"(WR) WR Delay From Falling Edge of Clock, WR Low tDH<I>(WR) WR Delay From Falling Edge of Clock, WR High tw (WRl) Pulse Width, WR low [101 MI tDl(MI) M I Delay From Rising Edge of Clock, Mi low tDH (Mil MT Delay From Rising Edge of Clock, M I High RFSH tDl(RF) RFSH Delay From Rising Edge of Clock, RFSH low IDH (RF) RFSH Delay From Rising Edge of Clock, RFSH High WAIT Is (WT) WAIT Setup Time to Falling Edge of Clock 70 HALT tD(HT) HALT Delay Time Fro", Falling Edge of Clock INT ts (IT) INT Selup Time 10 Rising Edge of Clock > 80 NMI tw(NMl) Pulse Width, NM I low 80 BUSRO ts (BO) BUSRO Selup Time 10 Rising Edge of Clock 80 BUSAK IDl(BA) BUSAK Delay From Rising Edge of Clock, BUSAK low IDH (BA) BUSAK Delay From Falling Edge of Clock, BUSAK High RESET Is (RS) RESET Setup Time to Rising Edge of Clock 90 IF (C) Delay to Float (MREO, 10RO, RD and WR) tmr Mi Slable Prior to 10RO (lnterrupl Ack.) IIII NOTES: A. Data should be enabled onto the CPU data bus when RD is active. During interrupt acknowledge data should be enabled when MI and fORQ arc both active. B. All control signals are internally synchronized. so they may be totally asynchronous with respect 10 the clock. C. The RESET signal must be active for a minimum of 3 dock cycles. D. Output Delay vs. Loaded Capacitance Max Unit 1121 fJsec [EJ nsec 2000 osec 30 osee 145 osee 110 osee osee osee nsec nsee 230 osec 90 nsec osec nsee nsec nsee osee 100 osee 100 nsec 100 osee osee osee 90 osee 110 osee 100 osee 110 osec 100 osec 130 osee 100 osee 110 osee 80 osec 90 osee 100 osee osee 130 osee 130 osee 180 osee 150 osee nsec 300 nsec nsec nsec nsec 120 nsec 110 nsec nsec 100 nsec nsec Add 10nsee delay for each SOpf increase in load up to a maximum of 200pf for the data bus & 1 OOpf for address & control lines E. Although static by design. testing guarantees tw(,pH) of 200 I1sec maximum Test Condition C l = 50pF [IJ tacm = tw(<I>H) + If-75 [2J taei = tc -80 [3J Ica = tw(<I>l) + tr - 40 [4J tcaf= IW(<I>l) + tr - 60 C L = SOpF [5J tdem = te - 210 [6J tdci = tw(cJ>L) + tr - 210 [7J tedf = tw(cJ>L) + tr -80 C l =50pF [8J tw (MRl) = tc - 40 [9J tw(MRH) = tw(<I>H) + tf-30 C l =50pF C l = 50pF C L = 50pF C L = SOpF C L = SOpF C L = 50pF C l ~ 50pF TEST POINT load circuit for Output

A.C. Timing Diagram Timing measurements are made at the following voltages, unless otherwise specified: _tc_ tW(<I>H)1 'i> CLOCK OUTPUT INPUT FLOAT UU'L ---1 W 'I) --l tW('I>!.) A O-A15 to (AD) =x K I--tS'I> (0)-= I-tH I- OUT "I" "0" Vee -.6V .4SV 2.0 V .8 V 2.0 V .8V av to.S v ~ r"\\ ~ r-"\\ - -.~ - -' ~,. . .J,~-. -:x " --- ..,,--- tSf.(D)-i --i-~ It- , -C>+- ~ to (D) '- - ~r )o-tF (D) - } ~ .. tDL (Ml) tDH (Ml)- 1'= f- -teal r-..~ {( f- -tea I tDH (RF) I- _tedl tDL(RF)_ f-H / i'f tF (C) -hf [L.j.(Mi', fI tDH'I' (MRl- _ ~(MR) tDH'f> (MR)- i -f-taem v~ !W(MRL) (I II .... ~DL'I'(R~) n tDH'I' (RD)- _ tw(MRH) ,T tD~~(RD)- ); - -.. -_/ , II .... WR IT ")r _ I tDH·f.(WR) tDL'I. (lR) f::::. tQ -tmr ---' ,If ~ -taci- ',. _/ ~D) ;'I~ )_ f t'l!:. il- l); h. DH'I'(WR) I tS(WT) tH tdci 1-::" Its (IT) tH --'-'- tW(~ ~ tH '-- ____ :x ,.-----, X ... _- tDH (BA) tDL (BA) tH ,-----....

A.C. Characteristics Z80A-CPU T A = oOe to 70°e, Vee = +5V ± 5'1<,. Unless Otherwise Noted. Signal Symbol Parameter Min Ie Clock Period .25 ~, Iw(<I>H) Clock Pulse Width, Clock High 110 Iw(<I>L) Clock Pulse Widlh, Clock Low 110 Ir,f Clock Rise and Fall Time ID(AD) Address Output Delay tF(AD) Delay to Float AO_IS tacm Address Stable Prior to MREQ (Memory Cycle) II tad Address Stable Prior to 10RQ; RD or WR (I/O Cycle) - tea Address Stable from RD. WR. 10RQ or MREO 3 leaf Address Stable From RD or WR During Float 141 ID(D) Data Output Delay IF (D) Delay to Float During Write Cycle tS<I>(D) Data Setup Time to Rising Edge of Clock During M I Cycle 3S DO_7 tS~(D) Data Setup Time to Falling Edge of Clock DUring M~ 10 M5 SO tdcm Data Stable Prior to WR (Memory Cycle) 5 tdci Data Stable Prior to WR (I/O Cyeie) 16 tcdf Data Stable From WR 171 tH Any Hold Time for Setup Time tDL~(MR) MREQ Delay From Falling Edge of Clock, MREQ Low tDH<I> (MR) MREQ Delay From Rising Edge of Clock, MREQ High MREQ tDH~(MR) MREQ Delay From Falling Edge of Clock, MREQ High tw(MRL) Pulse Width, MREQ Low 18 tw(MRH) Pulse Width, MREQ High 191 tDL<I> (IR) 10RQ Delay From Rising Edge of Clock, (ORQ Low 10RQ tDL~(lR) 10RQ Delay From Falling Edge of Clock, 10RQ Low tDH<I> (IR) 10RQ Delay From Rising Edge of Clock, [ORQ High tDH~(lR) 10RQ Delay From Falling Edge of Clock, [ORQ High tDL<I> (RD) RD Delay From Rising Edge of Clock, RD Low RD tDL~(RD) RD Delay From Falling Edge of Clock, RD Low tDH<I> (RD) RD Delay From Rising Edge of Clock, RD High tDH~(RD) RD Delay From Falling Edge of Clock, RD High tDL<I> (WR) WR Deiay From Rising Edge of Clock, WR Low WR tDL~(WR) WR Delay From Falling Edge of Clock, WR Low tDH<I>(WR) WR Delay Fr~ Falling Edge of Clock, WR High tw(WRL) Pulse Width, WR.Low [101 MI tDL(Ml) M 1 Delay From Rising Edge of Clock, M I Low tDH (MI) Mi Delay From Rising Edge of Clock, M I High RFSH tDL(RF) RFSH Delay From Rising Edge of Clock, RFSH Low tDH(RF) RFSH Delay From Rising Edge of Clock, RFsH High WAIT ts(WT) WAIT Setup Time to Falling Edge of Clock 70 HALT tD(HT) HALT Delay Time From Falling Edge of Clock lNT ts(IT) [NT Setup Time to Rising Edge of Clock 80 NM[ tw(NML) Pulse Width, NMI Low 80 BUSRQ ts(BQ) BUSRQ Setup Time to Rising Edge of Clock 50 BUSAK tDL(BA) BUSAK Delay From Rising Edge of Clock, BUSAK Low tDH(BA) BUSAK Delay From Falling Edge of Clock, BUSAK High RESET ts(RS) RESET Setup Time to Rising Edge of Clock 60 tF(C) Delay to Float (MREQ, (ORQ, RD and WR) tmr M 1 Stable Prior to [ORQ (Interrupt Ack.) 1111 NOTES: A. Dala should be enabled onto the CPU data bus when Ri5 is active. During interrupt ackrloWledge data should be ellabled when MT and (ORQ are both active. B. .All control signals are internally synchronized, so they may be totally asynchronous With respect to the clo.ck. C. The RESET signal must be active for a minimum of 3 clock cycles. D. Output Delay vs. Loaded Capacitance TA = 70°C Vcc = +5V ±5% Max II~I IE 2000 .10 110 150 90. 85 .. 95. .85 100 100 130 120 300 100 100 Add 1 Onsec delay for each 50pf increase in load up to maximum of 20Dpf for datil bus and i oope for address & control lines. E. A,lthoUgh static by design, testing gnarantees iw(<I>H) of 200 /lsec maidmum Unii Test Condition p5et: nsec [i2] tc '= tw(<I>H) + tw(<I>L) + tr + tf "sec nsec osec osec osec C L = 50pF nsec [I) tacm = tw(cI>H) + If - 65 "sec nsec (2) laci = tc ~70 nsec (3) tca = tw(tl>L) + tr - 50 osec nsec nsec C L = SOpl; nsec (4) tcaf= tw(<I>L) + tr-45 (5) tdcm" tc ~ 170 ns/!<:: [6] tdcl = tw(cJ>L) + tr - 170 nsec [7] tcdf = tw(cJ>L) + tt - 70 osec "sec "sec (' L = SOpF osec [81 tw (MiL)" tc - 30 nsec [9j tw(MRH) = tw(<I>H) + tf-20 nsec nsec CL = 50pF nsec nsec osec. nsec C L " 50pF osec osec osec nsec C L = 50pF osec osec nsec C L = 50pF osec nsec C L " 50pF osec osec osec CL = 50pF osec osec nsec osec C L = 50pF osec .. , osec ce··· nsec nset; tEST POINT Load Circuit for butptit

12.0 DECIV Decrement IV

DEC 55 Decrement Reg. pair 55 Zilog INSTRUCTION SET 01 Disable interrupts ADC HL, 55 Add with Carry Reg. pair ss to H L DJNZ e Decrement B and Jump relative if B/O ADC A,s Add with carry operand s to Acc. EI Enable interrupts ADD A, n Add value n to Acc. EX (SPl, HL Exchange the location (SP) and HL ADD A, r Add Reg. r to Acc. EX (SP), IX Exchange the location (SP) and IX ADD A, (HL) Add location (HL) to Acc. EX (SP), IV Exchange the location (SP) and IV ADD A, (lX+d) Add location (lX+d) to Acc. EX AF, AF' Exchange the contents of AF ADD A, (lV+d) Add location (lV+d) to Acc. and AF' ADD HL, ss Add Reg. pair ss to HL EX DE, HL Exchange the contents of DE and HL ADD IX, pp Add Reg. pair pp to IX EXX Exchange the contents of BC, DE, ADD IV, rr Add Reg. pair rr to IV HL with contents of BC', DE', HL' ANDs Logical 'AND' of operand sand Acc. respectively BIT b, (HL) Test BIT b of location (HL) HALT HALT (wait for interrupt or reset) BIT b, (lX+d) Test BIT b of location (lX+d) .IMO Set interrupt mode 0 BIT bi (lV+d) Test BIT b of location (lV+d) 1M 1 Set interrupt mode 1 BITb,r Test BIT b of Reg. r 1M2 Set interrupt mode 2 CALL cc, nn Call subroutine at location nn if IN A, (n) Load the Acc. with input from condition cc if true device n CALL nn Unconditional call subroutine at IN r, (C) Load the Reg. r with input from • location nn device (C) CCF Complement carry flag INC (HL) Increment location (HL) CP s Compare operand s with Acc. INCIX Increment IX CPO Compare location (HL) and Acc. INC (IX+d) Increment location (lX+d) decrement H Land BC INC IV I ncrement I V CPDR Compare location (HL) and Acc. decrement HL and BC, repeat INC (lV+d) Increment location (lV+d) until BC=O INC r Increment Reg. r CPI Compare location (HL) and Acc. INC ss increment HL and decrement BC Increment Reg. pair ss CPIR Compare location (HU and Acc. IND Load location (H L) with input increment H l, decrement BC from port (C), decrement HL and B repeat until BC=O CPL Complement Acc. (1 's coinp) INDR Load location (HL) with input from port (C), decrement HL and DAA Decimal adjust Acc. decrement B, repeat until B=O DECm Decrement operand in INI Load location (HL) with input from port (C); and increment HL DECIX Decrement I X and decrement B

INIR load location (Hl) with input lD (nn), A load location (nn) with Acc. from port (C), increment Hl lD (nn), dd load location (nn) with Reg. pair dd and decrement B, repeat until B=O lD (nn), Hl load location (nn) with Hl JP (HL) Unconditional Jump to (Hl) lD (nn), IX load location (nn) with IX JP (IX) Unconditional Jump to (IX) lD (nn), IV load location (nn) with IV JP (IV) Unconditonal Jump to (IV) lD R,A load R with Ace. JP cc, nn Jump to location nn if lD r, (Hl) load Reg. r with loca.ion (Hl) condition cc is true JP nn Unconditional jump to location lD r,(lX+d) load Reg. r with location (lX+d) nn lD r, (lV+d) load Reg. r with location (lV+d) JP C, e Jump relative to PC+e if carry=1 lD r, n load Reg. r with value n JR e Unconditional Jump relative lD r, r' load Reg.r with Reg. r' to PC+e lD SP, Hl load SP with H l JP NC, e Jump relative to PC+e if carry=O lD SP, IX load SP with I X JR NZ, e Jump relative to PC+e if non zero (Z=O) lD SP, IV load SP with IV JR Z, e Jump relative to PC+e if zero (Z=1) lDD load location (DE) with location (Hl), decrement DE, Hl and BC lD A, (BC) load Acc. with location (BC) lDDR load location (DE) with location lD A, (DE) load Acc. with location (DE) (Hl), decrement DE, Hl and BC; ( repeat until BC=O lDA,1 load Acc. with I lD A, (nn) load Acc. with IQcation nn lDI load location (DE) with location (HU, increment DE, Hl, lOA, R load Ace. with Reg. R decrement BC LD (BC), A load location (BC) with Ace. lDIR load location (DE) with location (Hl), increment DE, Hl, lD (DE), A load location (DE) with Acc. decrement BC and repeat until lD (Hl), n load location (Hl) with value n BC=O lD dd, nn load Reg. pair dd with value nn NEG Negate Ace. (2's complement) NOP No operation lD Hl, (nnL load Hl with location (nn) load location (HL) with Reg. r ORs logical 'OR' or operand s and Ace. lD (HL), r OTDR load output port (C) with location lD I,A load I with Acc. (Hl) decrement Hl and B, repeat until B=O IF IX, nn load I X with value nn OTIR load output port (C) with location lD IX, (nn) load IX with location (nn) (Hl), increment I1l, decrement B, lD (lX+d), n load location (lX+d) with value n repeat until B=O lD (lX+d), r load location (lX+d) with Reg. r OUT (C), r load output port (C) with Reg. r OUT (n), A load output port (n) with Acc. lD IV, nn load IV with value nn OUTD load output port (C) with location lD IV, (nn) load IV with location (nn) (Hl), decrement Hl and B lD (lV+d), n load location (lV+d) with value n OUTI load output port (C) with location (H L), increment H l and decrement lD (lV+d), r load location (lV+d) with Reg. r B

POP IX Load IX with top of stack RRm Rotate right through carry operand m POP IV Load IV with top of stack RRA Rotate right Ace. through carry POPqq Load Reg. pair qq with top of stack RRCm Rotate operand m right circular PUSH IX Load IX onto stack RRCA Rotate right circular Ace. PUSH IV Load IV onto stack RRD Rotate digit right and left between Ace. and location (HL) PUSH qq Load Reg. pair qq onto stack RES b, m Reset Bit b of operand m RSTp Restart to location p RET Return from subroutine SBC A, 5 Subtract operand 5 from Ace. with carry RETcc Return from subroutine if condition cc is true SBC HL, 55 Subtract Reg. pair S5 from HL with carry RETI Return from interrupt SCF Set carry flag (C=1) RETN Return from non ma5kable interrupt SET b, (HL) Set Bit b of location (HL) RLm Rotate left through carry operand m SET b, (lX+d) Set Bit b of location (lX+d) RLA Rotate left Ace. through carry SET b, (lV+d) Set Bit b of location (lV+d) RLC (HL) Rotate location (HL) left circular RLC (lX+d) Rotate location (lX+d) left circular SET b, r Set Bit b of Reg. r SLAm Shift operand m left arithmetic RLC (lV+d) Rotate location (lV+d) left circular SRAm Shift operand m right arithmetic RLCr Rotate Reg. r left circular SRL m Shift operand m right logical RLCA Rotate left circular Ace. SUB s Subtract operand s from Ace. RLD Rotate digit left and right between Ace. arid location (HL) XOR5 Exclusive 'OR' operand 5 and Ace.

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