X76F640 Datasheet, PDF (6/17 Pages) Xicor Inc. – Secure SerialFlash

X76F640
ACK Polling
Once a stop condition is issued to indicate the end of the
host’s write sequence, the X76F640 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 X76F640 is still busy with the
nonvolatile 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.
Data ACK Polling Sequence
WRITE SEQUENCE
COMPLETED
ENTER ACK POLLING
ISSUE START
ISSUE NEW
COMMAND
CODE
ACK
NO
RETURNED?
YES
PROCEED
7025 FM 08
After the password sequence, there is always a nonvola-
tile 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 X76F640
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.
Password ACK Polling Sequence
PASSWORD LOAD
COMPLETED
ENTER ACK POLLING
ISSUE START
ISSUE
PASSWORD
ACK COMMAND
ACK
RETURNED?
YES
PROCEED
NO
7025 FM 09
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 password is
incorrect until the 10ms write cycle time has elapsed.
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