X76F641 datasheet(6/17 Pages) ICMIC

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X76F641

ACK Polling

Once a stop condition is issued to indicate the end of the

host’s write sequence, the X76F641 initiates the internal

nonvolatile write cycle. In order to take advantage of the

typical 5ms write cycle, ACK polling can begin

immediately. This involves issuing the start condition

followed by the new command code of 8 bits (1st byte of

the protocol.) If the X76F641 is still busy with the non

volatile write operation, it will issue a “no-A

CK” in

response. If the nonvolatile write operation has completed,

an “ACK” will be returned and the host can

then proceed with the rest of the protocol.

After the password sequence, there is always a nonvolatile

write cycle. This is done to discourage random

guesses of the password if the device is being tampered

with. In order to continue the transaction, the

X76F641

requires the master to perform an ACK polling with the

specific code of F0h. As with regular Acknowledge polling

the user can either time out for 10ms, and then issue the ACK

polling once, or continuously loop as described in

the flow.

If the password that was inserted was correct, then an

“ACK” will be returned once the nonvolatile cycle is over,

in response to the ACK polling cycle immediately following

it.

If the password that was inserted was incorrect, then a

“no ACK” will be returned even if the nonvolatile cycle is

over. Therefore, the user cannot be certain that the pass-

word is incorrect until the 10ms write cycle time has

elapsed.

Data ACK Polling Sequence

ACK

RETURNED

ISSUE NEW

COMMAND

CODE

WRITE SEQUENCE

COMPLETED

ENTER ACK POLLING

ISSUE START

YES

PROCEED

7025 FM 08

Password ACK Polling Sequence

ACK

RETURNED

ISSUE

PASSWORD

ACK COMMAND

PASSWORD LOAD

COMPLETED

ENTER ACK POLLING

ISSUE START

YES

PROCEED

7025 FM 09

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