HCS320

DS41097C-page 14

© 2001 Microchip Technology Inc.

6.0

PROGRAMMING THE HCS320

When using the HCS320 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 cycle 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 S2 line

has been held high for the appropriate length of time

line (Table 6-1 and Figure 6-1). After the Program

mode is entered, a delay must be provided to the

device for the automatic bulk write cycle to complete.

This will set all locations in the EEPROM to zeros . The

device can then be programmed by clocking in 16 bits

at a time, using S2 as the clock line and PWM as the

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

gramming delay is required for the internal program

end of the programming cycle, the device can be veri-

fied (Figure 6-2) by reading back the EEPROM. Read-

ing is done by clocking the S2 line and reading the data

bits on PWM. For security reasons, it is not possible to

execute a verify function without first programming the

EEPROM. A Verify operation can only be done

once, immediately following the Program cycle.

FIGURE 6-1:

PROGRAMMING WAVEFORMS

FIGURE 6-2:

VERIFY WAVEFORMS

Note:

To ensure that the device does not acci-

dentally enter Programming mode, PWM

should never be pulled high by the circuit

connected to it. Special care should be

taken when driving PNP RF transistors.

PWM

Enter Program

Mode

(Data)

(Clock)

Note 1: Unused 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

Repeat for each word (12 times)

S2

Data for Word 0 (KEY_0)

Data for Word 1

PWM

(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

Data from Word 0

S2

Bit 0

Bit191

Bit190