X76F400

Characteristics subject to change without notice.

5 of 14

REV 1.0 7/5/00

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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.

ACK

Returned?

Issue Password

ACK Command

Password Load

Completed Enter ACK

Polling

Issue START

NO

YES

PROCEED