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SCS152

KEELOQ Token Card Chip

Microchip Technology 

SCS152

3.4 BITPROG

The BITPROG command modifies one bit in the

EEPROM. In the digit area, this command decrements

the current digit or in the CFG field it programs the bits

to AD(0) xor FUSE-BLOWN state: PC0 is erased to a

‘1’; PC1 is written to a ‘0’; LOCK0 is written to a ‘0’,

when the fuse is in blown state. Everywhere else in the

memory map, the current bit is written to a ‘0’.

Figure 3-4 diagrams the BITPROG command.

This command is signaled by pulsing SCI high. If the

operation is allowed, the SDIO line goes high. The

actual EEPROM modification is initiated by pulsing

SCK high. When the programming operation has been

completed, and SCK is low, the output goes low, indi-

cating that the command has completed.

TABLE 3-4: BITPROG FUNCTIONS

Field

Description

CID

SER

D4…D0

CFG

USER0

UKEY0

Writes current bit to ‘0’

Writes current bit to ‘0’

Decrements the current digit

Program the current bit to the value of

(AD(0) xor FUSE-BLOWN)

Writes current bit to ‘0’

Writes current bit to ‘0’

3.5 ERASE

The waveforms for ERASE are the same as BITPROG;

the command is implicitly coded by the repetition of the

sequence of events.

The ERASE command executes different functions,

depending on the current address as shown in

Table 3-5:

TABLE 3-5: ERASE FUNCTIONS

Field

Description

CID

SER

O4…O1

CFG

USER0

UKEY0

—

—

Sets the next digit to the maximum digit

value

—

0x6C…0x73: Erases current nibble to

all ‘1’ state

0x74…0x93: Erases the current byte to

all ‘1’ state

Erases the current byte to all ‘1’ state

FIGURE 3-4: BITPROG

SCI

SCK

SDIO

TC TS TC

TH

TPROG

DS40150B-page 8

Preliminary

© 1997 Microchip Technology Inc.

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