X46402 Datasheet, PDF (11/23 Pages) Xicor Inc. – Dual Voltage CPU Supervisor with 64K Password Protected EEPROM

X46402
ACK Polling
Once a stop condition is issued to indicate the end of the
host’s write sequence, the X46402 initiates the internal
nonvolatile write cycle. In order to take advantage of the
typical 5ms write cycle, ACK polling can begin immedi-
ately. This involves issuing the start condition followed by
the new command code of 8 bits (1st byte of the protocol.)
If the X46402 is still busy with the nonvolatile write opera-
tion, it will issue a “no-ACK” 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 proto-
col. See Figure 12.
Data ACK Polling Sequence
WRITE SEQUENCE
COMPLETED
ENTER ACK POLLING
ISSUE START
Preliminary Information
Password ACK Polling Sequence
PASSWORD LOAD
COMPLETED
ENTER ACK POLLING
ISSUE START
ISSUE
PASSWORD
ACK COMMAND
ACK
NO
RETURNED?
YES
PROCEED
ISSUE NEW
COMMAND
CODE
ACK
NO
RETURNED?
YES
PROCEED
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.
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 X46402 requires the mas-
ter 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.
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