HCS360

HCS360 MICROCHIP | Alldatasheet

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Technical content

ª 1996 Microchip Technology Inc. Preliminary DS40152C-page 1 M Code Hopping Encoder

FEATURES

• Programmable 28/32-bit serial number
• Programmable 64-bit encryption key
• Each transmission is unique
• 67-bit transmission code length
• 32-bit hopping code
• 35-bit fixed code (28/32-bit serial number, 4/0-bit function code, 1-bit status, 2-bit CRC)
• Encryption keys are read protected Operating
• 2.0-6.6V operation
• Four button inputs - 15 functions available
• Selectable baud rate
• Automatic code word completion
• Battery low signal transmitted to receiver
• Nonvolatile synchronization data
• PWM and Manchester modulation Other
• Easy to use programming interface
• On-chip EEPROM
• On-chip oscillator and timing components
• Button inputs have internal pull-down resistors
• Current limiting on LED output
• Minimum component count Enhanced Features Over HCS300
• 48-bit seed vs. 32-bit seed
• 2-bit CRC for error detection
• 28/32-bit serial number select
• Two seed transmission methods
• PWM and Manchester modulation
• IR modulation mode Typical Applications The HCS360 is ideal for Remote Keyless Entry (RKE) applications. These applications include:
• Automotive RKE systems
• Automotive alarm systems
• Automotive immobilizers
• Gate and garage door openers
• Identity tokens
• Burglar alarm systems PACKAGE TYPES HCS360 BLOCK DIAGRAM

DESCRIPTION

The HCS360 is a code hopping encoder designed for secure Remote Keyless Entry (RKE) systems. The HCS360 utilizes the K EE L OQ code hopping technology, which incorporates high security, a small package outline and low cost, to make this device a perfect solution for unidirectional remote keyless entry systems and access control systems. The HCS360 combines a 32-bit hopping code generated by a nonlinear encryption algorithm, with a 28/32-bit serial number and 7/3 status bits to create a 67-bit transmission stream. The length of the transmission eliminates the threat of code scanning and the code hopping mechanism makes each transmission unique, thus rendering code capture and resend (code grabbing) schemes useless. VDD LED PWM VSS PDIP, SOIC HCS360 VSS VDD Oscillator Reset circuit LED driver Controller Power latching and switching Button input port 32-bit shift register EncoderEEPROM PWM LED S3 S2 S1 S0 HCS360 K EE L OQ is a registered trademark of Microchip Technology Inc.

ª 1996 Microchip Technology Inc. The encryption key, serial number, and configuration data are stored in EEPROM which is not accessible via any external connection. This makes the HCS360 a very secure unit. The HCS360 provides an easy to use serial interface for programming the necessary security keys, system parameters, and configuration data. The encryption keys and code combinations are pro- grammab le but read-protected. The keys can only be verified after an automatic erase and programming operation. This protects against attempts to gain access to keys and manipulate synchronization values. The HCS360 operates over a wide voltage range of 2.0V to 6.6V and has four button inputs in an 8-pin configuration. This allows the system designer the freedom to utilize up to 15 functions. The only components required for device operation are the but- tons and RF circuitry, allowing a very low system cost.

1.0 SYSTEM O VER VIEW

1.1 K ey Terms

• Man ufacturer’s code – a 64-bit word, unique to each manufacturer, used to produce a unique encryption key in each transmitter (encoder).
• Encryption Key – a unique 64-bit key generated and programmed into the encoder during the man ufacturing process. The encryption key controls the encryption algorithm and is stored in EEPR OM on the encoder device.
• Learn – The HCS product family facilitates several learning strategies to be implemented on the decoder. The following are examples of what can be done. Normal Learning The receiver uses the same information that is transmitted during normal operation to derive the transmitter’s secret key, decrypt the discrimination value and the synchronization counter. Secure Learn* The transmitter is activated through a special but- ton combination to transmit a stored 48-bit value (random seed) that can be used for key genera- tion or be part of the key. Transmission of the ran- dom seed can be disabled after learning is completed. The HCS360 is a code hopping encoder device that is designed specifically for keyless entry systems, primarily for vehicles and home garage door openers. It is meant to be a cost-effective, yet secure solution to such systems. The encoder portion of a keyless entry system is meant to be held by the user and operated to gain access to a vehicle or restricted area. The HCS360 requires very few e xternal components (Figure 2-1). Most keyless entry systems transmit the same code from a transmitter every time a button is pushed. The relative number of code combinations for a low end sys- tem is also a relatively small number. These shortcomings provide the means for a sophisticated thief to create a device that ‘grabs’ a transmission and retransmits it later or a device that scans all possible combinations until the correct one is found. The HCS360 employs the K EE L OQ code hopping tech- nology and an encryption algorithm to achieve a high level of security. Code hopping is a method by which the code transmitted from the transmitter to the receiver is different every time a button is pushed. This method, coupled with a transmission length of 67 bits, virtually eliminates the use of code ‘grabbing’ or code ‘scanning’. As indicated in the block diagram on page one, the HCS360 has a small EEPROM array which must be loaded with several parameters before use. The most important of these values are:
• A 28/32-bit serial number which is meant to be unique for every encoder
• An encryption key that is generated at the time of production
• A 16-bit synchronization value The serial number for each transmitter is programmed by the manufacturer at the time of production. The generation of the encryption key is done using a key generation algorithm (Figure 1-1). Typically, inputs to the key generation algorithm are the serial number of the transmitter or seed value, and a 64-bit manufac- turer’s code. The manufacturer’s code is chosen by the system man ufacturer and must be carefully controlled. The manufacturer’s code is a pivotal part of the overall system security. The 16-bit synchronization value is the basis for the transmitted code changing for each transmission, and is updated each time a button is pressed. Because of the complexity of the code hopping encryption algo- rithm, a change in one bit of the synchronization value will result in a large change in the actual transmitted code. There is a relationship (Figure 1-2) between the key values in EEPROM and how they are used in the encoder. Once the encoder detects that a button has been pressed, the encoder reads the button and updates the synchronization counter. The synchroniza- tion value is then combined with the encryption key in the encryption algorithm and the output is 32 bits of encrypted information. This data will change with every button press, hence, it is referred to as the hopping portion of the code word. The 32-bit hopping code is combined with the button information and the serial number to form the code w ord transmitted to the receiver. The code word format is explained in detail in Section 4.2. *Secure Learning patents pending.

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 3 Any type of controller may be used as a receiver, but it is typically a microcontroller with compatible firmw are that allows the receiver to operate in conjunction with a transmitter, based on the HCS360 . Section 7.0 provides more detail on integrating the HCS360 into a total system. Before a transmitter can be used with a particular receiver, the transmitter must be ‘learned’ by the receiver. Upon learning a transmitter, information is stored by the receiver so that it may track the transmitter, including the serial number of the transmitter, the current synchronization value for that transmitter and the same encryption key that is used on the transmitter. If a receiver receives a message of valid format, the serial number is checked and, if it is from a learned transmitter, the message is decrypted and the decrypted synchronization counter is checked against what is stored. If the synchronization value is verified, then the button status is checked to see what operation is needed. Figure 1-3 shows the relationship between some of the values stored by the receiver and the val- ues received from the transmitter. FIGURE 1-1: CREATION AND STORA G E OF ENCR YPTION K EY DURING PR ODUCTION FIGURE 1-2: BASIC OPERATION OF TRANSMITTER (ENCODER) FIGURE 1-3: BASIC OPERATION OF RECEIVER (DECODER) Transmitter Man ufacturer’s Serial Number or Code Encryption Key Key Generation Algorithm Serial Number Encryption Key Sync Counter HCS360 EEPR OM Array Seed KEE LOQ Algorithm Button Press InformationEncryption EEPR OM Array

32 Bits of

Encrypted Data Serial Number Transmitted Information Decryption Key Sync Counter Serial Number Button Press Information EEPR OM Array Decryption Key Encrypted DataSerial Number Received Information Decrypted Synchronization Counter Check for Match Check for Match KEE LOQ Algorithm De cryption Sync Counter Serial Number Man ufacturer Code

ª 1996 Microchip Technology Inc.

2.0 DE VICE OPERATION

As shown in the typical application circuits (Figure 2-1), the HCS360 is a simple device to use. It requires only the addition of buttons and RF circuitry for use as the transmitter in your security application. A description of each pin is described in Table 2-1. FIGURE 2-1: TYPICAL CIR CUITS TABLE 2-1 PIN DESCRIPTIONS The high security level of the HCS360 is based on the patented K EE L OQ technology. A block cipher type of encryption algorithm based on a block length of 32 bits and a key length of 64 bits is used. The algorithm obscures the information in such a way that even if the transmission information (before coding) differs by only one bit from the information in the previous transmis- sion, the next coded transmission will be totally differ- ent. Statistically, if only one bit in the 32-bit string of information changes, approximately 50 percent of the coded transmission will change. The HCS360 will wake up upon detecting a switch closure and then delay approximately 6.5 ms for switch debounce (Figure 2-2). The synchronization information, fixed information, and switch information will be encrypted to form the hopping code. The encrypted or hopping code portion of the transmission will change every time a b utton is pressed, even if the same button is pushed again. Keeping a button pressed for a long time will result in the same code word being transmitted until the button is released or time-out occurs. A code that has been transmitted will not occur again for more than 64K transmissions. This will provide more than 18 years of typical use before a code is repeated based on 10 oper- ations per day. Ov erflow information programmed into the encoder can be used by the decoder to extend the number of unique transmissions to more than 128K. If, in the transmit process, it is detected that a new but- ton(s) has been pressed, a reset will immediately be forced and the code word will not be completed. Please note that buttons removed will not have any effect on the code word unless no buttons remain pressed in which case the current code word will be completed and the pow er down will occur. Name Pin Number Description S0 1 Switch input 0 S1 2 Switch input 1 S2 3 Switch input 2/Can also be clock pin when in programming mode S3 4 Switch input 3/C lock pin when in programming mode V SS

5 Ground reference connection

PWM 6 Pulse width modulation (PWM) output pin/Data pin for programming mode LED 7 Cathode connection for directly driving LED during transmission V DD

8 Positive supply voltage

5 button remote control (Note) B4 B3 B2 B1 B0 Note: Up to 15 functions can be implemented by pressing more than one button simulta- neously or by using a suitable diode array.

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 5 FIGURE 2-2: ENCODER OPERATION

3.0 EEPR OM MEMOR Y

The HCS360 contains 192 bits (12 x 16-bit words) of EEPR OM memor y (Table 3-1). This EEPROM array is used to store the encr yption key information, synchronization value, etc. Further descriptions of the memor y array is given in the following sections. TABLE 3-1 EEPR OM MEMOR Y MAP

3.1 K ey_0 - Key_3 (64-Bit Encryption Key)

The 64-bit encryption key is used by the transmitter to create the encrypted message transmitted to the receiver. This key is created and programmed at the time of production using a key generation algorithm. Inputs to the key generation algorithm are the serial number for the particular transmitter being used and a secret manufacturer’s code. While the key generation algorithm supplied from Microchip is the typical method used, a user may elect to create their own method of key generation. This may be done providing that the decoder is programmed with the same means of creat- ing the key for decryption purposes. If a seed is used, the seed will also form part of the input to the key gen- eration algorithm. Pow er Up Reset and Debounce Delay (6.5 ms) Sample Inputs Update Sync Info Encrypt With Load Transmit Register Buttons Added All Buttons Released (A button has been pressed) Transmit Stop No Yes No Yes Encryption Key Complete Code W ord Transmission W ORD ADDRESS MNEMONIC DESCRIPTION

0 KEY_0 64-bit encryption

key (w ord 0)

1 KEY_1 64-bit encryption

key (w ord 1)

2 KEY_2 64-bit encryption

key (w ord 2)

3 KEY_3 64-bit encryption

key (w ord 3)

4 SYNC_A 16-bit synchroniza-

5 SYNC_B/S EED _2 16-bit synchroniza-

(word 2)

6 RESER VED Set to 0000H

7 SE ED_ 0 Seed Value (w ord 0)

8 SE ED_ 1 Seed Value (w ord 1)

7 SE R_ 0 Device Serial

Number (w ord 0)

10 SE R_ 1 Device Serial

Number (w ord 1)

11 CONFIG Configuration W ord

ª 1996 Microchip Technology Inc.

3.2 SYNC_A, SYNC_B

(Synchronization Counter) This is the 16-bit synchronization value that is used to create the hopping code for transmission. This value will be changed after every transmission. A second syn- chronization value can be used to stay synchronized with a second receiver.

3.3 SEED_0, SEED_1, and SEED_2

(Seed W ord) This is the three word (48 bits) seed code that will be transmitted when seed transmission is selected. This allows the system designer to implement the secure learn feature or use this fixed code word as part of a different key generation/tracking process or purely as a fixed code transmission.

3.4 SER_0, SER_1

(Encoder Serial Number) SER_0 and SER_1 are the low er and upper words of the device serial number, respectively. There are 32 bits allocated for the serial number and a selectable config- uration bit determines whether 32 or 28 bits will be transmitted. The serial number is meant to be unique for every transmitter.

3.5 CONFIG

(Configuration W ord) The configuration word is a 16-bit word stored in EEPR OM array that is used by the device to store information used during the encryption process, as well as the status of option configurations. Fur ther explanations of each of the bits are described in the following sections.

3.5.1 LNGRD: LONG GUARD TIME

LNGRD = 1 selects the encoder to extend the guard time between code words. This can be used to reduce the average pow er transmitted over a 100ms window and thereby transmit a higher peak pow er.

3.5.2 FAST 1, FAST 0 BAUD RATE SELECTION

FAST 1 and FAST 0 selects the baud rate according to Table 3-3. TABLE 3-3 BAUD RATE SELECTION TABLE 3-2 CONFIGURATION W OR D Bit Number Symbol Bit Description

0 LNGRD Long Guard Time

1 FAST 0 Baud Rate Selection

2 FAST 1 Baud Rate Selection

3 NU Not Used

4 SEED Seed Transmission enable

5 DELM Delay mode enable

6 TIMO Time out enable

7 IND Independent mode enable

8 USRA0 User bit

9 USRA1 User bit

10 USRB0 User bit

11 USRB1 User bit

12 XSER Extended serial number

13 TMPSD Temporary seed transmis-

14 MANCH Manchester/PWM modula-

15 O VR Ov erflow bit

T E FAST 1 FAST 0 400 0 0 200 0 1 200 1 0 100 1 1

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 7

3.5.3 SEED: ENAB LE SEED TR ANSMISSION

If SEED = 0, seed transmission is disabled. The inde- pendent counter mode can only be used with seed transmission disabled since SEED_2 is shared with the second synchronization counter. W ith SEED = 1, seed transmission is enabled. The appropriate button code(s) must be activated to trans- mit the seed information. In this mode, the seed infor- mation (SEED_0, SEED_1, and SEED_2) and the upper 12- or 16-bits of the serial number (SER_1) are transmitted instead of the hop code. Seed transmission is available for function codes (Table 3-7) S[3:0] = 1001 and S[3:0] = 0011(delayed). This takes place regardless of the setting of the IND bit. The two seed transmissions are shown in Figure 3-1. FIGURE 3-1: SEED TRANSMISSION All examples shown with XSER = 1, SEED = 1 When S[3:0] = 1001, delay is not acceptable. CRC+ VLOW SER_1 SEED_2 SEED_1 SEED_0 Data transmission direction For S[3:0] = 0x3 before delay: 16-bit Data W ord 16-bit Counter Encrypt CRC+ VLOW SER_1 SER_ 0 Encrypted Data For S[3:0] = 0011 after delay (Note 1, Note 2): CRC+ VLOW SER_1 SEED_2 SEED_1 SEED_0 Data transmission direction Data transmission direction Note 1:For Seed Transmission, SEED_2 is transmitted instead of SER_0. 2: For Seed Transmission, the setting of DELM has no effect.

ª 1996 Microchip Technology Inc.

3.5.4 DELM: DELAY MODE

If DELM = 1, delay transmission is enabled. A delayed transmission is indicated by inverting the low er nibble of the discrimination value. The delay mode is primarily for compatibility with previous K EE L OQ de vices. I f DELM = 0, delay transmission is disabled (Table 3-4).

3.5.5 TIMO: TIME-OUT

If TIMO = 1, the time-out is enabled. Time-out can be used to terminate accidental continuous transmissions. When time-out occurs, the PWM output is set low and the LED is turned off. Current consumption will be higher than in standby mode since current will flow through the activated input resistors. This state can be exited only after all inputs are taken low. TIMO = 0, will enable continuous transmission (Table 3-5). TABLE 3-4 TYPICAL DELA Y TIMES FAST1 FAST0 Number of Code W ords before Delay Mode Time Before Delay Mode (MANCH = 0) Time Ref Delay Mode (MANCH = 1) 0 0 28 2.9s 5.1s 0 1 56 3.1s 6.4s 1 0 28 1.5s 3.2s 1 1 56 1.7s 4.5s TABLE 3-5 TYPICAL TIME-OUT TIMES FAST 1 FAST 0 Maxim um Number of Code W ords Transmitted Time Before Time-out (MANCH = 0) Time Before Time-out (MANCH = 1) 0 0 256 26.5s 46.9 0 1 512 28.2s 58.4 1 0 256 14.1s 29.2 1 1 512 15.7s 40.7

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 9

3.5.6 IND: INDEPENDENT MODE

The independent mode can be used where one encoder is used to control tw o receivers. Tw o counters (SYNC_A a nd SYNC_B) are used in independent mode . As indicated in Table 3-7, function codes 1 to 7 use SYNC_A and 8 to 15 SYNC_B . The independent mode also selects IR mode. In IR mode function codes 12 to 15 will use SYNC_B . The PWM output signal is modulated with a 40 kHz carrier. It must be pointed out the 40 kHz is derived from the internal clock and will therefore vary with the same percentage as the baud rate. If IND = 0, SYNC_A is used for all function codes. If IND = 1, independent mode is enabled and counters for functions are used according to Table 3-7. For IND = 1 and S[3:0] 0xC, 0xD, 0xE, 0xF, Basic Pulse Width modulation becomes:

3.5.7 USRA,B: USER BITS

User bits form part of the discrimination value. The user bits together with the IND bit can be used to identify the counter that is used in independent mode.

3.5.8 XSER: EXTENDED SER IAL NUMBER

If XSE R = 1, the full 32-bit serial number [SER_1, SER _0] is transmitted. If XSER = 0, the four most sig- nificant bits of the serial number are substituted by S[3:0] and is compatible with the HCS200/300/301.

3.5.9 TMPSD: TEMPOR AR Y SEED

The temporary seed transmission can be used to dis- able learning after the transmitter has been used for a programmab le number of operations. This feature can be used to implement very secure systems. After learn- ing is disabled, the seed information cannot be accessed even if physical access to the transmitter is possible. If TMPSD = 1 the seed transmission will be disabled after a number of code hopping transmissions. The number of transmissions before seed transmission is disabled, can be programmed b y setting the synchro- nization counter (SYNC_A, SYNC_B) to a value as shown in Table . TABLE 3-6 SYNC HR ONOUS COUNTER INITIALIZATION VALUES Sync hronous Counter Values Number of Transmissions 0000H 128 0060H 64 0050H 32 0048H 16 TABLE 3-7 FUNCTION CODES S3 S2 S1 S0 IND = 0 IND = 1 Comments Counter 1 0 0 0 1 A A 2 0 0 1 0 A A 3 0 0 1 1 A A If SEED = 1, transmit seed after delay. 4 0 1 0 0 A A 5 0 1 0 1 A A 6 0 1 1 0 A A 7 0 1 1 1 A A 8 1 0 0 0 A B 9 1 0 0 1 A B If SEED = 1, transmit seed immediately. 10 1 0 1 0 A B 11 1 0 1 1 A B 12 1 1 0 0 A B IR mode 13 1 1 0 1 A B IR mode 14 1 1 1 0 A B IR mode 15 1 1 1 1 A B IR mode

DS40152C -page 10 Preliminary ª 1996 Microchip Technology Inc.

3.5.10 MANCH: MANCHESTER CODE

MANCH selects between Manchester code modulation and PWM modulation. If MANCH = 1, Manchester code modulation is selected: If MANCH = 0, PWM modulation is selected.

3.5.11 O VR: OVERFLO W

The overflow bit is used to extend the number of possi- ble synchronization values. The synchronization counter is 16 bits in length, yielding 65,536 values before the cycle repeats. Under typical use of 10 operations a day, this will provide nearly 18 years of use before a repeated value will be used. Should the system designer conclude that is not adequate, then the overflow bit can be utilized to extend the number of unique values. This can be done by programming OVR to 1 at the time of production. The encoder will automat- ically clear OVR the first time that the transmitted syn- chronization value wraps from 0xFFFF to 0x0000. Once cleared, OVR cannot be set again, thereby creat- ing a permanent record of the counter overflow. This prevents fast cycling of 64K counter. If the decoder sys- tem is programmed to track the overflow bits, then the effective number of unique synchronization values can be extended to 128K. If programmed to zero, the sys- tem will be compatible with the NTQ104/5/6 devices (i.e., no overflow with discrimination bits set to zero).

4.0 TRANSMITTED W OR D

4.1 Transmission Format (PWM)

The HCS360 transmission is made up of several parts (Figure 4-1 and Figure 4-2). Each transmission is begun with a preamble and a header, follow ed by the encrypted and then the fixed data. The actual data is 67 bits which consists of 32 bits of encrypted data and 35 bits of fixed data. Each transmission is follow ed by a guard period before another transmission can begin. Refer to Table 8-4 and Table 8-5 for transmission timing specifications. The encrypted portion provides up to four billion changing code combinations and includes the function bits (based on which buttons were acti- vated) along with the synchronization counter value and discrimination value. The non-encrypted portion is comprised of the CRC bits, VLOW bits, the function bits and the 28/32-bit serial number. The encrypted and non-encrypted sections combined increase the number of combinations to 1.47 x 1020.

4.2 Code W ord Organization

The HCS360 transmits a 67-bit code word when a but- ton is pressed. The 67-bit word is constructed from a Fixed Code portion and an Encrypted Code portion (Figure 4-3). The Encrypted Data is generated from 4 function bits, 2 user bits, overflow bit, independent mode bit, and 8 serial number bits, and the 16-bit synchronization value (Figure 8-4). The Non-encrypted Code Data is made up of a VLOW bit, 2 CRC bits, 4 function bits, and the 28-bit serial number. If the extended serial number (32 bits) is selected, the 4 function code bits will not be transmit- ted.

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 11 FIGURE 4-1: TRANSMISSION FORMAT—MANCH = 0 FIGURE 4-2: TRANSMISSION FORMAT—MANCH = 1 FIGURE 4-3: CODE W OR D ORGANIZA TION (RIGHT-MOST BIT IS CLOCKED OUT FIR ST) LOGIC "1" Code W ord Guard TimePreamb le Sync Encrypted TX Data Fixed Code Data BIT LOGIC "0" 3 5 7 9 4 6 8 10 TE CODE W ORD: TO TAL TRANSMISSION: Preamb le Sync Encrypt Fixed Guard

1 CODE W ORD

TimePreamb le Sync Encrypted D ata Fixed Code Data LOGIC "0" BPW CODE W ORD: TO TAL TRANSMISSION: Sync Encrypt Fixed Guard LOGIC "1" Start bit Stop bit CODE W ORD Preamb le Fixed Code Data Encrypted Code Data 67 bits of Data Transmitted MSB LSB CRC (2 bit) VLOW (1 bit) Button Status (4 bits) 28-bit Serial Number Button Status (4 bits) Discrimination bits (12 bits) 16-bit Synch Value CRC (2 bit) VLOW bit + Serial Number and Button Status (32 bits)+ 32 bits of Encrypted Data

DS40152C -page 12 Preliminary ª 1996 Microchip Technology Inc.

5.0 SPECIAL FEA TURES

5.1 Code W ord Completion

Code w ord completion is an automatic feature that ensures that the entire code word is transmitted, even if the button is released before the transmission is com- plete and that a minimum of two words are completed. The HCS360 encoder pow ers itself up when a button is pushed and pow ers itself down after two complete w ords are transmitted if the user has already released the button. If the button is held down beyond the time for one transmission, then multiple transmissions will result. If another button is activated during a transmission, the active transmission will be aborted and the new code will be generated using the new button information.

5.2 Long Gu ard Time

Federal Comm unications Commission (FCC) part 15 rules specify the limits on fundamental pow er and harmonics that can be transmitted. Pow er is calculated on the worst case average pow er transmitted in a 100ms windo w. It is therefore advantageous to minimize the duty cycle of the transmitted word. This can be achieved by minimizing the duty cycle of the individual bits and by extending the guard time between transmissions. long guard time (LNGRD) is used for reducing the average pow er of a transmission. This is a selectable feature. Using the LNGRD allows the user to transmit a higher amplitude transmission if the transmission time per 100 ms is shorter. The FCC puts constraints on the average po w er that can be transmitted by a de vice, and LNGRD effectively prevents continuous transmission by only allowing the transmission of every second word. This reduces the average pow er transmitted and hence, assists in FCC approval of a transmitter device.

5.3 CRC (Cyc le Redundancy Check) Bits

The CRC bits are calculated on the 65 previously trans- mitted bits. The CRC bits can be used by the receiver to check the data integrity before processing starts. The CRC can detect all single bit and 66% o f double bit errors. The CRC is computed as follows: EQ UATION 5-1: CRC CALCULATION and with and Din the nth transmission bit 0 £ n £ 64

5.4 Secure Learning

In order to increase the level of security in a system, it is possible for the receiver to implement what is known as a secure learning function. This can be done by utilizing the seed value on the HCS360 which is stored in EEPR OM . Instead of the normal key generation method being used to create the encryption key, this seed value is used and there should not be any mathematical rela- tionship between serial numbers and seeds for the best security.

5.5 Auto-shutoff

The A uto-shutoff function automatically stops the device from transmitting if a button inadvertently gets pressed for a long period of time. This will prevent the device from draining the battery if a button gets pressed while the transmitter is in a pocket or purse. This func- tion can be enabled or disabled and is selected by set- ting or clearing the time-out bit (Section 3.5.5). Setting this bit w ill enable the function (turn Auto-shutoff func- tion on) and clearing the bit w ill disable the function. Time-out period is approximately 25 seconds.

5.6 VLOW : Voltage LOW Indicator

The VLOW bit is transmitted with every transmission (Figure 4-2) and will be transmitted as a one if the operating voltage has dropped below the low voltage trip point, approximately 3.8V at 25°C. This VLOW signal is transmitted so the receiver can give an indication to the user that the transmitter battery is low.

5.7 LED Output Operation

During normal transmission the LED output is LOW . If the supply voltage drops below the low voltage trip point, the LED output will be toggled at approximately 1Hz during the transmission. C R C 1[ ]n 1+ C R C 0[ ]n D inÙ= C R C 0[ ]n 1+ C R C 0[ ]n D inÙ( ) C R C 1[ ]nÙ= C R C 1 0,[ ]0 0=

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 13

6.0 PR OGRAMMING THE HCS360

When using the HCS360 in a system, the user will have to program some parameters into the device including the serial number and the secret key before it can be used. The programming allows the user to input all 192 bits in a serial data stream, which are then stored internally in EEPROM. Programming will be initiated by forcing the PWM line high, after the S3 line has been held high for the appropriate length of time. S0 and S1 should be held low during the entire program cycle (Table 6-1 and Figure 6-1). The device can then be pro- grammed b y clocking in 16 bits at a time, follow ed by the word’s complement using S3 or S2 as the clock line and PWM as the data in line. After each 16-bit word is loaded, a programming delay is required for the internal program cycle to complete. The acknowledge can read back after the programming delay (TWC ). After the first w ord and its complement have been downloaded, an automatic bulk write is performed. This delay can take up to Twc. At the end of the programming cycle, the device can be verified (Figure 6-2) by reading back the EEPR OM. Reading is done by clocking the S3 line and reading the data bits on PWM. For security reasons, it is not possible to execute a verify function without first programming the EEPR OM. A verify operation can only be done once, immediately following the pro- gram cycle. FIGURE 6-1: PR OGRAMMING W A VEF ORMS FIGURE 6-2: VERIFY W A VEF ORMS TABLE 6-1 PR OGRAMMING/VERIFY TIMING REQUIREMENTS VDD = 5.0V – 10% 25° C – 5 °C Parameter Symbol Min. Max. Units Program mode setup time T2 0 4.0 ms Hold time 1 T1 9.0 — ms Program cycle time TWC — 30 ms Clock low time TCLKL 25 — ms Clock high time TCLKH 25 — ms Data setup time TDS 0 — ms Data hold time TDH 18 — ms Data out valid time TDV — 24 ms PWM Enter Program Mode (Data) (Clock) Bit 0 Bit 1 Bit 2 Bit 3 Bit 14Bit 15 Bit 16Bit 17 Repeat 12 times for each word TCLKH TCLKL TWCTDS S2/S3 Data for W ord 0 (KEY_0) Data for W ord 1 TDH Bit 0 Bit 1 Bit 2 Bit 3 Bit 14Bit 15 Note 1:Un used button inputs to be held to ground during the entire programming sequence. 2: The VDD pin must be taken to ground after a program/verify cycle. Acknowledge PWM (Clock) (Data) Note: If a Verify operation is to be done, then it must immediately follow the Program cycle. End of Programming Cycle Begin Verify Cycle Here Bit 1Bit 2 Bit 3 Bit 15Bit 14 Bit 16Bit 17 Bit190Bit191 TWC Data in W ord 0 TDV S2/S3 Bit 0Bit191Bit190

DS40152C -page 14 Preliminary ª 1996 Microchip Technology Inc.

7.0 INTEGRATING THE HCS360

Use of the HCS360 in a system requires a compatible decoder. This decoder is typically a microcontroller with compatible firmw are. Firmw are routines that accept transmissions from the HCS360 and decrypt the hopping code portion of the data stream are available. These routines provide system designers the means to develop their own decoding system.

7.1 Learning a Transmitter to a Receiver

In order for a transmitter to be used with a decoder, the transmitter must first be ‘learned’. Several learning strategies can be follow ed in the decoder implementa- tion. When a transmitter is learned to a decoder, it is suggested that the decoder stores the serial number and current synchronization value in EEPROM. The decoder must keep track of these values for every transmitter that is learned (Figure 7-1). The maximum number of transmitters that can be learned is only a function of how m uch EEPR OM memor y storage is available. The decoder must also store the manufac- turer’s code in order to learn a transmission transmitter, although this value will not change in a typical system so it is usually stored as part of the microcontroller R OM code . Storing the manufacturer’s code as part of the ROM code is also better for security reasons. It must be stated that some learning strategies have been patented and care must be taken not to infringe. FIGURE 7-1: TYPICAL LEARN SEQUENCE Enter Learn Mode W ait for Reception of a Valid Code Generate Key from Serial Number Use Generated Key to Decrypt Compare Discrimination Value with Fixed Value Equal W ait for Reception of Second Valid Code Compare Discrimination Value with Fixed Value Use Generated Key to Decrypt Equal Counters Encryption key Serial number Synchronization counter Sequential Exit Learn successful Store: Learn Unsuccessful No No No Yes Yes Yes

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 15

7.2 Decoder Operation

In a typical decoder operation (Figure 7-2), the key gen- eration on the decoder side is done by taking the serial number from a transmission and combining that with the manufacturer’s code to create the same secret key that was used by the transmitter. Once the secret key is obtained, the rest of the transmission can be decrypted. The decoder waits for a transmission and immediately can check the serial number to determine if it is a learned transmitter. If it is, it takes the encrypted portion of the transmission and decrypts it using the stored key It uses the discrimination bits to determine if the decryption was valid. If everything up to this point is valid, the synchronization value is evaluated. FIGURE 7-2: TYPICAL DECODER OPERATION

7.3 Sync hronization with Decoder

The KEE LOQ technology features a sophisticated synchronization technique (Figure 7-3) which does not require the calculation and storage of future codes. If the stored counter value for that particular transmitter and the counter value that was just decrypted are within a formatted window of say 16, the counter is stored and the command is executed. If the counter value was not within the single operation window, but is within the double operation window of say 32K window, the trans- mitted synchronization value is stored in temporary location and it goes back to waiting for another trans- mission. When the next valid transmission is received, it will check the new value with the one in temporary storage. If the two values are sequential, it is assumed that the counter had just gotten out of the single opera- tion ‘window’, but is now back in sync, so the new syn- chronization value is stored and the command executed. If a transmitter has somehow gotten out of the double operation window, the transmitter will not w ork and must be relearned. Since the entire window rotates after each valid transmission, codes that have been used are part of the ‘blocked’ (32K) codes and are no longer valid. This eliminates the possibility of grab- bing a previous code and retransmitting to gain entry. FIGURE 7-3: SYNC HR ONIZATION WINDO W Transmission Received Does Serial Number Match Decrypt Transmission Is Decryption Valid Is Counter Within 16 Is Counter Within 32K Update Counter Execute Command Save Counter in Temp Location Start No No No No Yes Yes Yes Yes Yes No andNo Note: The synchronization method described in this section is only a typical implementation and because it is usually implemented in firmw are, it can be altered to fit the needs of a particular systemBlocked Entire Window rotates to eliminate use of previously used codes CurrentPosition (32K Codes) Doub le Operation (32K Codes) Single Operation Window (16 Codes)

DS40152C -page 16 Preliminary ª 1996 Microchip Technology Inc.

8.0 ELECTRICAL CHARA CTERISTICS

TABLE 8-1 ABSOLUTE MAXIMUM RA TINGS Symbol Item Rating Units VDD Supply voltage -0.3 to 6.9 V VIN Input voltage -0.3 to VDD + 0.3 V VOUT Output voltage -0.3 to VDD + 0.3 V IOUT Max output current 25 mA TSTG Storage temperature -55 to +125 °C (Note) TLSOL Lead soldering temp 300 °C (Note) VESD ESD rating 4000 V Note: Stresses above those listed under “ABSOLUTE MAXIMUM RA TINGS” may cause permanent damage to the device. TABLE 8-2 DC CHARA CTERISTICS Commercial (C): Tamb = 0°C to +70°C Industrial (I):Tamb = -40°C to +85°C 2.0V < VDD < 3.3 3.0 < VDD < 6.6 Parameter Sym. Min Typ

1 Max Min Typ

1 Max Uni

Operating current (avg) ICC 0.3 1.2 0.7 1.6 mA VDD = 3.3V VDD = 6.6V Standby current ICCS 0.1 1.0 0.1 1.0 mA Auto-shutoff current2,3 ICCS 40 75 160 350 mA High level Input voltage VIH 0.55VD D VDD +0. 0.55VD D VDD +0. V Low level input voltage VIL -0.3 0.15VD D -0.3 0.15VD D V High level output voltage VOH 0.7VDD 0.7VDD V IOH = -1.0mA, VDD = 2.0V IOH = -2.0mA, VDD = 6.6V Low level output voltage VOL 0.08VD D 0.08VD D V IOL = 1.0mA, VDD = 2.0V IOL = 2.0mA, VDD = 6.6V Resistance; S0-S3 RS0- 40 60 80 40 60 80 kW VDD =4.0V Resistance; PWM RPW M 80 120 160 80 120 160 kW VDD =4.0V Note 1:Typical values are at 25°C. 2: Auto-shutoff current specification does not include the current through the input pulldown resistors. 3: Auto-shutoff current is periodically sampled and not 100% tested.

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 17 FIGURE 8-1: PO WER UP AND TRANSMIT TIMING FIGURE 8-2: PWM F ORMAT (MANCH = 0) FIGURE 8-3: PWM PREAMB LE/HEADER F ORMAT TABLE 8-3 PO WER UP AND TRANSMIT TIMING REQUIREMENTS VDD = +2.0 to 6.6V Commercial(C): Tamb = 0°C to +70°C Industrial (I):Tamb = -40°C to +85°C Parameter Symbol Min Max Unit Remarks Time to second button press TBP 10 + Code W ord Time 26 + Code W ord Time ms (Note 1) Transmit delay from button detect TTD 4.5 26 ms (Note 2) Debounce delay TDB 4.0 13 ms Auto-shutoff time-out period TTO 15.0 35 s (Note 3) Note 1:TBP is the time in which a second button can be pressed without completion of the first code word and the intention was to press the combination of buttons. 2: Transmit delay maximum value if the previous transmission was successfully transmitted. 3: The auto shutoff timeout period is not tested. Button Press Sn Detect TDB PWM TTD Code W ord Transmission TTO Code W ord Code W ord Code W ord Code W ord n TBP LOGIC ‘0’ LOGIC ‘1’ Preamb le Header Encrypted Portion of Transmission Fixed portion of Transmission Guard Time TP TH THOP TFIX TG TBP TE TE TE Preamb le Header

32 TE 10 TE

DS40152C -page 18 Preliminary ª 1996 Microchip Technology Inc. FIGURE 8-4: PWM DATA W OR D FORMAT FIGURE 8-5: MANC HESTER F ORMAT (MANCH = 1) FIGURE 8-6: MANC HESTER PREAMB LE/HEADER F ORMAT Bit 0 Bit 1 Header Bit 30Bit 31Bit 32Bit 33 Bit 58Bit 59 Fixed Code DataEncrypted Data Guard LSBLSB MSB MSB S3 S0 S1 S2 VLOW CRC0 CRC1 Time Serial Number Function Code Status Bit 60Bit 61Bit 62Bit 63Bit 64Bit 65 CRC Bit 66 LOGIC ‘0’ LOGIC ‘1’ Preamb le Header Encrypted Portion of Transmission Fixed portion of Transmission Guard TimeTP TH THOP TFIX TG TBP TE TE Preamb le Header

32 TE 4 TE

FIGURE 8-7: HCS360 NORMALIZ ED TE VS. TEMP 0.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.7 0.6 TE Min. TE Max. VDD LEGEND = 2.0V = 3.0V = 6.0V Typical TE Temperature °C -50-40 -30-20 -10 0 10 20 30 40 50 60 70 80 90

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 19 TABLE 8-4 CODE W OR D TRANSMISSION TIMING PARAMETER S—PWM MODE VDD = +2.0V to 6.6V Commercial (C):Tamb = 0°C to +70°C Industrial (I):Tamb = -40°C to +85°C Code W ords Transmitted FAST1 = 0, FAST0 = 0 FAST1 = 0, FAST0 = 1 Symbol Characteristic Number of TE Min. Typ. Max. Number of TE Min. Typ. Max. Units TE Basic pulse element 1 260 400 620 1 130 200 310 ms TBP PWM bit pulse width 3 780 1200 1860 3 390 600 930 ms — PWM data rate — 1282 833 538 — 2564 1667 1075 bps Note: The timing parameters are not tested but derived from the oscillator clock. VDD = +2.0V to 6.6V Commercial (C):Tamb = 0°C to +70°C Industrial (I):Tamb = -40°C to +85°C Code W ords Transmitted FAST1 = 1, FAST0 = 0 FAST1 = 1, FAST0 = 1 Symbol Characteristic Number of TE Min. Typ. Max. Number of Te Min. Typ. Max. Units TE Basic pulse element 1 130 200 310 1 65 100 155 ms TBP PWM bit pulse width 3 390 600 930 3 195 300 465 ms — PWM data rate — 2564 1667 1075 — 5128 3333 2151 bps Note: The timing parameters are not tested but derived from the oscillator clock.

ª 1996 Microchip Technology Inc. TABLE 8-5 CODE WORD TRANSMISSION TIMING PARAMETERS—MANCHESTER MODE V DD = +2.0V to 6.6V Commercial (C):Tamb = 0 C to +70 C Industrial (I):Tamb = -40 C to +85 C Code Words Transmitted FAST1 = 0, FAST0 = 0 FAST1 = 0, FAST0 = 1 Symbol Characteristic Number of T E Min. Typ. Max. Number of Te Min. Typ. Max. Units T E Basic pulse element 1 520 800 1240 1 260 400 620 m s T P T H T START T HOP T FIX T STOP T G — Manchester data rate — 1923 1250 806 — 3846.2 2500 1612.9 bps Note: The timing parameters are not tested but derived from the oscillator clock. V DD = +2.0V to 6.6V Commercial (C):Tamb = 0 C to +70 C Industrial (I):Tamb = -40 C to +85 C Code Words Transmitted FAST1 = 1, FAST0 = 0 FAST1 = 1. FAST0 = 1 Symbol Characteristic Number of T E Min. Typ. Max. Number of Te Min. Typ. Max. Units T E Basic pulse element 1 260 400 620 1 130 200 310 m s T P T H T START T HOP T FIX T STOP T G Note: The timing parameters are not tested but derived from the oscillator clock.

ª 1996 Microchip Technology Inc. Preliminary DS40152C -page 21 NOTES:

DS40152C -page 22 Preliminary ª 1996 Microchip Technology Inc. NOTES:

ª 1996 Microchip Technology Inc. Preliminary DS40152C-page 23 HCS360 PRODUCT IDENTIFICATION SYSTEM To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office. Sales and Support Package: P = Plastic DIP (300 mil Body), 8-lead SN = Plastic SOIC (150 mil Body), 8-lead Temperature Blank = 0˚C to +70˚C Range: I = –40˚C to +85˚C Device: HCS360 Code Hopping Encoder HCS360T Code Hopping Encoder (Tape and Reel) HCS360 — /P Data Sheets Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recom- mended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following: 1. Y our local Microchip sales office (see last page) 2. The Microchip Corporate Literature Center U.S. FAX: (602) 786-7277 3. The Microchip’s Bulletin Board, via your local CompuServe number (CompuServe membership NOT required). Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using.

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