X46402V8-3.1 XICOR [Xicor Inc.], X46402V8-3.1 Datasheet - Page 11

• Manufacturer Part Number: X46402V8-3.1
• Description: Dual Voltage CPU Supervisor with 64K Password Protected EEPROM
• Manufacturer: XICOR [Xicor Inc.]

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.
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.
X46402
Data ACK Polling Sequence
ENTER ACK POLLING
WRITE SEQUENCE
RETURNED
ISSUE START
ISSUE NEW
COMPLETED
COMMAND
PROCEED
CODE
ACK
YES
?
NO
11
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.
Password ACK Polling Sequence
ENTER ACK POLLING
PASSWORD LOAD
ACK COMMAND
Preliminary Information
ISSUE START
COMPLETED
RETURNED
PASSWORD
PROCEED
ISSUE
ACK
YES
?
NO