© 1996 Microchip Technology Inc.

Preliminary

DS21143A-page 11

HCS301

6.0

PROGRAMMING THE HCS301

When using the HCS301 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 S3 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

write all locations in the EEPROM to an all zeros pat-

tern. The device can then be programmed by clocking

in 16 bits at a time, using S3 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. This delay can take up to Twc. At the

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 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

EEPROM. A verify operation can only be done

immediately following the program cycle.

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.

FIGURE 6-1:

PROGRAMMING WAVEFORMS

FIGURE 6-2:

VERIFY WAVEFORMS

TABLE 6-1:

PROGRAMMING/VERIFY TIMING REQUIREMENTS

± 10%

25

° C ± 5 °C

Parameter

Symbol

Min.

Max.

Units

Program mode setup time

3.5

4.5

ms

Hold time 1

3.5

—

ms

Hold time 2

—

µs

Bulk Write time

—

2.2

ms

Program delay time

—

2.2

ms

Program cycle time

—36

ms

Clock low time

25

—

µs

Clock high time

25

—

µs

Data setup time

0—

µs

Data hold time

18

—

µs

Data out valid time

10

24

µs

PWM

Enter Program

Mode

(Data)

(Clock)

Bit 0

Bit 1

Bit 2

Bit 3

Bit 14

Bit 15

Bit 16

Bit 17

Repeat 12 times for each word

S3

Data for Word 0 (KEY_0)

Data for Word 1

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

PWM

(Clock)

(Data)

End of

Programming Cycle

Begin Verify Cycle Here

Bit 1 Bit 2

Bit 3

Bit 15

Bit 14

Bit 16 Bit 17

Bit190 Bit191

Data in Word 0

S3

Bit 0

Bit191

Bit190

Note:

If a verify operation is to be done, then it must immediately follow the program cycle.