X76F400 Datasheet, PDF (5/14 Pages) IC MICROSYSTEMS – Secure SerialFlash

X76F400
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 X76F400
requires the master to perform a password ACK polling
sequence with the specific command code of 55h. 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 inserted is correct, the nonvolatile cycle
in response to the password ACK polling
sequence is over, and an “ACK” is returned.
If the password inserted is incorrect, a “no ACK” is
returned, even if the nonvolatile cycle is over. There-
fore, the user cannot be certain that the password is
incorrect until the 10ms write cycle time has elapsed.
Password ACK Polling Sequence
READ OPERATIONS
Read operations are initiated in the same manner as
write operations but with a different command code.
Sector Read
With sector read, a sector address is supplied with the read
command. Once the password has been
acknowledged data may be read from the sector. An
acknowledge must follow each 8-bit data transfer. A
read operation always begins at the first byte in the
sector, but may stop at any time. Random accesses to
the array are not possible. Continuous reading from the
array will return data from successive sectors. After
reading the last sector in the array, the address is auto-
matically set to the first sector in the array and data can
continue to be read out. After the last bit has been read,
a stop condition is generated without sending a
preceding acknowledge.
Password Load
Completed Enter ACK
Polling
Issue START
Issue Password
ACK Command
ACK
NO
Returned?
YES
PROCEED
REV 1.0 7/5/00
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Characteristics subject to change without notice. 5 of 14