HCS412SN datasheet(34/44 Pages) MICROCHIP

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HCS412

DS41099C-page 34

Preliminary

7.0

PROGRAMMING THE HCS412

The HCS412 requires some parameters programmed

into the device before it can be used. The programming

cycle allows the user to input all 288 bits in a serial data

stream, which are then stored internally in EEPROM.

Programming is initiated by forcing the DATA line high,

after the S2 line has been held high for the appropriate

length of time line (Table 7-1 and Figure 7-2).

A delay is required after entering Program mode while

the automatic bulk erase cycle completes. The bulk

erase writes all EEPROM locations to zeros.

The device is then programmed by clocking in the

EEPROM memory map (Least Significant bit first) 16

bits at a time, using S2 as the clock line and DATA as

the data-in line. After each 16-bit word is loaded, a pro-

gramming delay is required for the internal program

cycle to complete. This delay can take up to Twc.

The HCS412 will signal a ‘write complete’ after writing

each 16-bit word by sending out a series of ACK pulses

TACKH high, TACKL low on DATA. The ACK pulses con-

tinue until S2 is dropped.

Programming verification is allowed only once, after the

programming cycle (Figure 7-3), by reading back the

EEPROM memory map. Reading is done by clocking

the S2 line and reading the data bits on DATA, again

Least Significant bit first. For security reasons, it is not

possible to execute a Verify function without first pro-

gramming the EEPROM.

FIGURE 7-1:

CREATION AND STORAGE OF CRYPT KEY DURING PRODUCTION

FIGURE 7-2:

PROGRAMMING WAVEFORMS

FIGURE 7-3:

VERIFY WAVEFORMS

Note:

To ensure that the device does not acci-

dentally enter Programming mode, DATA

should never be pulled high by the circuit

connected to it. Special care should be

taken when driving PNP RF transistors.

Transmitter

Manufacturer’s

Serial Number

Code

Crypt

Key

Generation

Algorithm

Serial Number

Crypt Key

Sync Counter

HCS412

Production

Programmer

EEPROM Array

DATA

Enter Program

Mode

(Data)

(Clock)

Note 1: S0 and S1 button inputs to be held to ground during the entire programming sequence.

Bit 0

Bit 1

Bit 2

Bit 3

Bit 14

Bit 15

Bit 16

Bit 17

TPH1

TPBW

TPS

Repeat for each word (18 times total)

TPH2

TCLKH

TCLKL

TWC

TDS

Data for Word 1

TDH

TCLKL

Initiate Data

Polling Here

Write Cycle

Complete Here

Calibration Pulses

Ack

Data for Word 0

(KEY1_0)

(KEY1_1)

DATA

(Clock)

(Data)

Note: If a Verify operation is to be done, then it must immediately follow the Program cycle.

End of Programming Cycle

Beginning of Verify Cycle

Bit 1 Bit 2

Bit 3

Bit 15

Bit 14

Bit 16 Bit 17

Bit190 Bit191

TWC

Data from Word 0

TDV

Bit 0

Bit191

Bit190

Ack

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