AN114

AN114 XICOR | Alldatasheet

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retrieved after power cycles. shorten the code by removing any unnecessary routines. Figure 1. Connecting the X9408 to an 80C51 microcontroller

www.xicor.com REV 1.1 11/12/02 master can now begin acknowledge polling by succes- sively sending start conditions followed by "dummy" instructions. When the X9408/X9418 finally answers with an acknowledge, the internal write cycle has been completed. The master must then initiate a stop condi- tion. After the next start condition, the X9408/X9418 is ready to receive further instructions. In the code listing, an assumption was made that the code executes upon a reset of the microcontroller. That is, the code is loaded into low memory, however this can be changed with an ORG assembler directive. Simple MAIN program routines are included in the code listing. These can be modified for different device addresses, different registers and different DCPs within the device. In this listing, the commands cause an X9408/X9418 (at A3A2A1A0 = 1100 to be accessed.) The listing also includes some instructions that are specific to the Cygnal 80C51 processor. These should be examined and modi- fied, as needed, for the specific 80C51 in the system. The commands issued in the “Main” section of the code are simple assignment and call sequences. In Figure 1, a representative hardware connection between the X9408 and an 8051 family microcontroller is shown. The pull-up resistors on the SDA and SCL lines are determined by the total capacitance of all of the devices connected to the bus, which is about 18pF. 80C51 MICROCONTROLLER ROUTINES FOR MANIPULATING AN X9408 ; 80C51 MICROCONTROLLER ROUTINES FOR MANIPULATING AN X9408 ; QUAD EEPOT ; (C) XICOR INC. 2002 ; CEM ; FILE NAME : X9408_8051.TXT ; TARGET MCU: Cygnal C8051F000 ; DESCRIPTION: ; This code provides basic 80C51 code for commmunicating with and ; controlling the X9408 quad digital potentiometer. In this listing ; is code that implements all of the available X9408 instructions. ; The X9408 communicates via a 2-wire bus that is similar, but a little ; different from the I2C bus. This code is very generic and can be ; simplified and shortened by removing any unnecessary routines. ; For those instructions which program the nonvolatile data registers ; (XFR_WCR, GFXR_WCR, and WRITE_DR) this program provides acknowledge ; polling to determine early completion of the internal write cycle. ; Although this is handled automatically by the routines, some background ; might be helpful. ; After issuing a start condition, the master sends a slave address ; and receives and acknowledge (ACK). The master then sends an instruction ; byte to the X9408 and again receives an ACK. If necessary, the master sends ; a data byte and receives a final ACK. The master then initiates a stop ; condition to signal the X9408 to begin an internal nonvolatile write ; cycle. When the write cycle begins, the I/O pins go to a high impedance state ; and remain in this state until the nonvolatile write is complete. ; Immediately following the stop condition, the master can begin acknowledge ; polling by successively sending start conditions, followed by "dummy" ; instructions. When the X9408 finally answers with an acknowledge, the ; internal write cycle is completed. The master then issues a stop ; condition. After the next start condition, the X9408 is ready to receive ; further instructions.

www.xicor.com REV 1.1 11/12/02 ; This code give the flexibility to communicate with up to 16 different X9408 ; devices on the same bus. It does this by using a register, named "ADDR_BYTE". ; This register is loaded with the specific slave address and address of the ; desired X9408 device. The register can be saved if there is only one X9408 ; on the bus, by making ADDR_BYTE a constant. ; An 80C51 register is used to identify the particular X9408 register or DCP, or both, ; are used for a particular operation. There are various constants available for ; easy selection of the WCR and DR combination. The contents of the register ; is appended to the specific instruction in the "instr_gen' routine. ; A register is used as a counter for keeping track of the number of bits sent ; in each byte. ; A register is used for the increment/decrement instruction to specify up or ; down movement of the wiper. For each command, the master loads the "PULSES" ; register with a direction bit and 6 bits of count. If the MSB is a 1 ; the wiper increments the specified number of tap positions. If the MSB ; is a 0 the wiper decrements the specified number of tap positions. ; A register is used to hold the specific command being executed. This allows ; the instruction to be built up and sent to the X9408. ; In the MAIN section are sample main code segments showing how to use the ; various subroutines. ; This code was tested on a Cygnal 80C51 microcontroller, using the Cygnal ; tools. The specific routines required to set up the Cygnal processor ; are identified and are probably not needed for other standard 8051 devices. ; Since each 8051 may have specific requirements that are not handled in this ; code, the programmer is advised to check the setup needs of the specific ; 80C51 derivation that is being used. ; I/O Definition SCL bit p1.0 ; 80C51 pin used AS SCL SDA bit p1.1 ; 80C51 pin used AS SDA ; Register Definition $include (c8051f000.inc); Include regsiter definition file (Cygnal). TEMP equ r1 ; Scratch register COUNT equ r2 ; Loop counting register PULSES equ r3 ; Bits -> DIR 0 ###### (#=pulses = 0 to 64) ID equ r5 ; Bits -> 0 0 0 0 R1 R0 P1 P0 ADDR_BYTE equ r6 ; Bits -> 0 1 0 1 A3 A2 A1 A0 DATA_BYTE equ r7 ; Bits -> CM DW D5 D4 D3 D2 D1 D0 ; Constant Definition SLAVE_ADR0 equ 050h SLAVE_ADR1 equ 051h SLAVE_ADR2 equ 052h SLAVE_ADR3 equ 053h SLAVE_ADR4 equ 054h SLAVE_ADR5 equ 055h SLAVE_ADR6 equ 056h

www.xicor.com REV 1.1 11/12/02 SLAVE_ADR7 equ 057h SLAVE_ADR8 equ 058h SLAVE_ADR9 equ 059h SLAVE_ADR10 equ 05Ah SLAVE_ADR11 equ 05Bh SLAVE_ADR12 equ 05Ch SLAVE_ADR13 equ 05Dh SLAVE_ADR14 equ 05Eh SLAVE_ADR15 equ 05Fh WCR_0 equ 00h WCR_1 equ 01h WCR_2 equ 02h WCR_3 equ 03h DR_0 equ 00h DR_1 equ 04h DR_2 equ 08h DR_3 equ 0Ch DCP0_R0 equ 00h DCP0_R1 equ 04h DCP0_R2 equ 08h DCP0_R3 equ 0Ch DCP1_R0 equ 01h DCP1_R1 equ 05h DCP1_R2 equ 09h DCP1_R3 equ 0Dh DCP2_R0 equ 02h DCP2_R1 equ 06h DCP2_R2 equ 0Ah DCP2_R3 equ 0Eh DCP3_R0 equ 03h DCP3_R1 equ 07h DCP3_R2 equ 0Bh DCP3_R3 equ 0Fh READWCR equ 0 WRITEWCR equ 4 READDR equ 8 WRITEDR equ 12 XFRDR equ 16 XFRWCR equ 20 GXFRDR equ 24 GXFRWCR equ 28 INCDECWIPER equ 32 ; INTERNAL RAM STACK_TOP equ 060H ; Stack top ; RESET and INTERRUPT VECTORS cseg AT 0 ljmp main ; Locate a jump to the start of code at

www.xicor.com REV 1.1 11/12/02 ; CODE SEGMENT Code_Seg segment CODE rseg Code_Seg Switch to this code segment. using Specify register bank for the following program code. ; NAME: execute ; FUNCTION: Determines which X9408 instruction is issued, ; then executes ; INPUTS: COMMAND ; OUTPUTS: none ; CALLS: read_wcr, read_dr, write_wcr, write_dr, xfr_dr, ; xfr_wcr, gxfr_dr, gxfr_wcr, inc_wiper ; AFFECTED: DPTR, A execute: mov dptr,#first ; Get Base Address mov a,COMMAND ; Jump Offset jmp @a+dptr ; Jump to instruction handler first: call read_wcr ; COMMAND #0 ret call write_wcr ; COMMAND #4 ret call read_dr ; COMMAND #8 ret call write_dr ; COMMAND #12 ret call xfr_dr ; COMMAND #16 ret call xfr_wcr ; COMMAND #20 ret call gxfr_dr ; COMMAND #24 ret call gxfr_wcr ; COMMAND #28 ret call inc_wiper ; COMMAND #32 ret ; The following routines handle each X9408 instruction. ; These are called by the "execute" routine. ; read_wcrReads a WCR and returns its value in DATA_BYTE ; write_wcrWrites the value in DATA_BYTE to a WCR ; read_drReads a Data Register and returns its value in DATA_BYTE ; write_drWrites the value in DATA_BYTE to a data register ; xfr_drTransfers the value in a data register to its WCR ; xfr_wcrTransfers the value in a WCR to one of its data registers ; gxfr_drGlobal transfer of data registers to WCRs ; gxfr_wcrGlobal transfer of WCRs to Data Registers ; inc_wiperSingle Step Increment/Decrement of wiper position for WCR

www.xicor.com REV 1.1 11/12/02 ; FUNCTION: Appends bits R1, R0, P1, P0 to the appropriate ; Instruction code and passes the instruction byte to the ; Instruction Generator. ; INPUTS: ID ; OUTPUTS: NONE ; CALLS: instr_gen ; AFFECTED: ID,A,DPTR read_wcr: mov a,ID ; Get bits x x P1 P0 orl a,#090h ; Append to read WCR instruction code mov ID,a ; Save the result mov dptr,#case1 ; Jump to the base addr for this instruciton call instr_gen ret write_wcr: mov a,ID ; Get bits x x P1 P0 orl a,#0A0h ; Append to Write WCR instruction code mov ID,a ; Save the result mov dptr,#case2 ; Jump to the base addr for this instruction call instr_gen ret read_dr: mov a,ID ; Get bits R1 R0 P1 P0 orl a,#0B0h ; Append to Read DR instruction code mov ID,a ; Save the result mov dptr,#case1 ; Jump to the base addr for this instruction call instr_gen ret write_dr: mov a,ID ; Get bits R1 R0 P1 P0 orl a,#0C0h ; Append to Write DR instruction code mov ID, a ; Save the result mov dptr,#case3 ; Jump to the base addr for this instruction call instr_gen ret xfr_dr: mov a,ID ; Get bits R1 R0 P1 P0 orl a,#0D0h ; Append to the XFR DR instruction code mov ID, a ; Save the result mov dptr,#case4 ; Jump to the addr for this instruction call instr_gen ret xfr_wcr: mov a,ID ; Get bits R1 R0 P1 P0 orl a,#0E0h ; Append to the XFR WCR instruction code mov ID, a ; Save the result mov dptr,#case5 ; Jump to the addr for this instruction call instr_gen ret gxfr_dr: mov a,ID ; Get bits R1 R0 x x orl a,#010h ; Append to the GXFR DR instruction code mov ID, a ; Save the result mov dptr,#case4 ; Jump to the addr for this instruction call instr_gen ret

www.xicor.com REV 1.1 11/12/02 gxfr_wcr: mov a,ID ; Get bits R1 R0 x x orl a,#080h ; Append to the GXFR WCR instruction code mov ID, a ; Save the result mov dptr,#case5 ; Jump to the addr for this instruction call instr_gen ret inc_wiper: mov a,ID ; Get bits x x P1 P0 orl a,#020h ; Append to the Incr Wiper instruction code mov ID,a ; Save the result mov dptr,#case6 ; Jump to the addr for this instruction call instr_gen ret ; NAME: instr_gen (Instruction generator) ; FUNCTION: Issues appropriate I2C protocol for each X9408 instruction ; INPUTS: ADDR_BYTE, ID, PULSES, DPTR, DATA_BYTE ; OUTPUTS: DATA_BYTE ; CALLS: start_cond, stop_cond, send_byte, send_bit, get_byte, polling ; AFFECTED: DATA_BYTE, A, COUNT instr_gen: call start_cond ; Issue an I2C start condition mov a,ADDR_BYTE ; Send X9408 slave/address byte call send_byte jc stop_gen ; if NACK, end... mov a,ID ; Send X9408 instruction byte call send_byte jc stop_gen ; if NACK, end... clr a ; Reset offset before jump jmp @a +dptr ; Jump to various instruction cases case6: mov a,PULSES ; A <- Bits DIR X D5 D4 D3 D2 D1 D0 anl a,#00111111b ; A <- Bits 0 0 D5 D4 D3 D2 D1 D0 mov COUNT, a ; Save as the number of pulses mov a,PULSES anl a,#10000000b ; A <- Bits DIR 0 0 0 0 0 0 0 wiper_lp: call send_bit ; Send the bit (a single pulse) djnz COUNT,wiper_lp ; Continue until all pulses are sent case4: jmp stop_gen ; If program gets here, then it is done case2: mov a,DATA_BYTE ; Send X9408 data byte call send_byte jmp stop_gen case1: call get_byte ; Receive X9408 Data Byte jmp stop_gen case3: mov a,DATA_BYTE ; Send X9408 Data Byte call send_byte

www.xicor.com REV 1.1 11/12/02 call stop_cond ; Issue a stop condition call polling ; Begin Acknowledge Polling jmp stop_gen case5: call stop_cond ; Issue a stop condition call polling ; Begin Acknowledge Polling stop_gen: call stop_cond ; I2C Transmission Over! ret ; NAME: send_byte ; FUNCTION: Sends 8 bits (from MSB to LSB) to SDA and reads 1 bit from SDA ; INPUTS: A ; OUTPUTS: NONE ; CALLS: send_bit, get_bit ; AFFECTED: COUNT, TEMP, A send_byte: mov COUNT,#8 ; Set loop for 8 repetitions mov TEMP,a ; store as shifted byte (no shift) bit_loop: mov a,TEMP ; Retrieve last saved shifted byte anl a,#10000000b ; Mask for MSB (Most Significant Bit) call send_bit ; Place this bit on SDA next_bit: mov a,TEMP ; Retrieve last saved shifted byte rl a ; Rotate all bits 1 position left mov TEMP,a ; Store this updated shifted byte djnz COUNT,bit_loop setb SDA ; let SDA go high after 8th bit call clock ; When all 8 bits done, read SDA line ; (ACKnowledge pulse) ret ; NAME: send_bit ; FUNCTION: Places a bit on SDA and initiates a clock pulse on SCL ; INPUTS: A ; OUTPUTS: NONE ; CALLS: clock ; AFFECTED: SDA send_bit: clr SDA ; Pull SDA Low jz sent_zero ; Should SDA really be LOW? setb SDA ; If Not, pull SDA HIGH sent_zero: call clock ; Initiate a clock pulse ret

www.xicor.com REV 1.1 11/12/02 ; NAME: clock ; FUNCTION: Issues a LOW-HIGH-LOW clock pulse of sufficient duration ; & reads SDA during the high phase, just in case its needed ; INPUTS: NONE ; OUTPUTS: C ; CALLS: NONE ; AFFECTED: SCL, C clock: nop ; Let SDA Set-up setb SCL ; Pull SCL HIGH and hold nop nop nop mov c,SDA ; Move SDA bit into carry flag clr SCL ; Pull SCL LOW ret ; NAME: get_byte ; FUNCTION: Receives 8 bits from SDA (MSB to LSB) and sends 1 bit to SDA ; INPUTS: NONE ; OUTPUTS: DATA_BYTE ; CALLS: clock, send_bit ; AFFECTED: COUNT, SDA, A, DATA_BYTE get_byte: setb SDA ; Receiver shouldn't drive SDA low mov COUNT,#8 ; Set Loop count to 8 repetitions get_loop: call clock ; Clock in the current bit rlc a ; Reconstruct byte using left shifts djnz COUNT,get_loop mov DATA_BYTE,a ; Store retrieved Byte for user clr a ; A <- LOW (Sending a 0) call send_bit ; Send an acknowledge ret ; NAME: start_cond (Start Condition) ; FUNCTION: Issues an I2C bus start condition ; INPUTS: NONE ; OUTPUTS: NONE ; CALLS: NONE ; AFFECTED: SDA, SCL start_cond: setb SDA ; Pull SDA HIGH and allow set-up setb SCL ; Pull SCL HIGH and hold nop nop nop nop clr SDA ;Pull SDA LOW (SCL=HIGH) and hold nop nop nop nop

www.xicor.com REV 1.1 11/12/02 clr SCL ;Complete clock pulse ret ; NAME: stop_cond (Stop condition) ; FUNCTION: Issues an I2C bus stop condition ; INPUTS: NONE ; OUTPUTS: NONE ; CALLS: NONE ; AFFECTED: SDA, SCL stop_cond: clr SDA ; Pull SDA LOW and hold setb SCL ; Pull SCL HIGH and hold nop nop nop nop setb SDA ; Pull SDA HIGH (SCL=HIGH) ret ; NAME: ack_send (Send Acknowledge) ; FUNCTION: Sends an acknowledge bit to complete SDA line data reads ; INPUTS: NONE ; OUTPUTS: NONE ; CALLS: send_bit ; AFFECTED: A ack_send: clr a ; A <- LOW (Sending a 0) call SEND_BIT ; Send the bit! ret ; NAME: polling (Acknowledge polling for XFR_WCR, WRITE_DR, GXFR_WCR) ; FUNCTION: Sends dummy commands to X9408 during an internal write cycle ; so that the end of the cycle is marked by an acknowledge ; INPUTS: ADDR_BYTE ; OUTPUTS: NONE ; CALLS: start_cond, send_byte ; AFFECTED: C polling: call START_COND ; Re-establish I2C protocol mov a,ADDR_BYTE ; Attempt to send a dummy command again: call SEND_BYTE jc POLLING ; If C=1, then there was no ACK ret

www.xicor.com REV 1.1 11/12/02 ; PUT MAIN PROGRAM HERE... ; Below are sample main programs calling the various command routines main: mov SP, #STACK_TOP; Initialize stack pointer ; The following section is required for the Cygnal processor. This could ; change for different versions of the 80C51. ; Disable the WDT. (IRQs not enabled at this point.) ; If interrupts were enabled, they would need to be explicitly disabled ; so that the 2nd move to WDTCN occurs no more than four clock ; cycles after the first move to WDTCN. clr EA ; Disable interupts mov WDTCN, #0DEh; Cygnal processor specific mov WDTCN, #0ADh; Cygnal processor specific ; Enable the Port I/O Crossbar mov XBR2, #40h ; Cygnal processor specific (enable weak pull ups) mov PRT1CF, #00h ; Cygnal processor specific ; Set no ports as push-pull (this processor ; operates from 3.3V, but the X9408 operates from ; 5V, so the 8051 outputs must be pulled up to 5V ; with external resistors.) ; The following are sample code segments for use in the main program... ; The potentiometer was A0-A3 pins were set to address 0Ch. write_2_wcr: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #WCR_2 ; Specify WCR for DCP#2 mov COMMAND, #WRITEWCR; Write to WCR mov DATA_BYTE, #43; Set wiper position to tap 43 call execute read_from_wcr: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #WCR_2 ; Specify WCR for DCP#2 mov COMMAND, #READWCR; Read WCR call execute ; WCR value is in DATA_BYTE write_2_dr: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #DCP2_R1; Specify DR#1 for DCP#2 mov COMMAND, #WRITEDR; Write to DR mov DATA_BYTE, #21; Set data value to 21 call execute

www.xicor.com REV 1.1 11/12/02 read_from_dr: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #DCP2_R1; Specify DR#1 for DCP#2 mov COMMAND, #READDR; Read DR call execute ; DR value is in DATA_BYTE mov_dr_2_wcr: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #DCP2_R1; Specify DR#1 to WCR of DCP#2 mov COMMAND, #XFRDR; Transfer DR to WCR call execute mov_wcr_2_dr: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #DCP2_R1; Specify WCR to DR#1 of DCP#2 mov COMMAND, #XFRWCR; Transfer WCRto DR call execute global_dr_2_wcr: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #DR_1 ; Specify DR#1 to WCR mov COMMAND, #GXFRDR; Transfer DR to WCR call execute global_wcr_2_dr: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #DR_1 ; Specify WCR to DR#1 of DCP#2 mov COMMAND, #GXFRWCR; Transfer WCRto DR call execute decr_wiper: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #WCR_2 ; Select DCP#2 mov PULSES, #0Fh; Decrement DCP#2 for 16 pulses mov COMMAND, #INCDECWIPER; INC wiper call execute incr_wiper: mov ADDR_BYTE, #SLAVE_ADR12; Load Slave address byte mov ID, #WCR_2 ; Select DCP#2 mov PULSES, #8Fh; Increment DCP#2 for 16 pulses mov COMMAND, #INCDECWIPER; DEC wiper call execute END