HCS200

DS40138D-page 10

© 2011 Microchip Technology Inc.

6.0

PROGRAMMING THE HCS200

When using the HCS200 in a system, the user will have

to program some parameters into the device, such as

the serial number and crypt 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 inter-

nally 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 (Table 6-1

and Figure 6-1). After the Program mode is entered, a

delay must be provided for the automatic bulk write

cycle to complete. This will write all locations in the

EEPROM to zeros. The device can then be pro-

grammed by clocking in 16 bits at a time, using S2 as

the clock line and PWM as the data in line; data is

clocked in on the falling edge of S2. After each 16-bit

word is sent, a programming delay of TWC is required

for the internal program cycle to complete. At the end

of the programming cycle, the device can be verified

(Figure 6-2) by reading back the EEPROM. Reading is

done by clocking the S2 line and reading the data bits

on PWM. The falling edge of S2 initiates the reading.

For security reasons, it is not possible to execute a Ver-

ify function without first programming the EEPROM. A

Verify operation can only be done immediately fol-

lowing 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 (result-

ing in a bulk erase), 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)

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

Note 1: Unused button inputs to be held to ground during the entire programming sequence.

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