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X76F128 Datasheet, PDF (6/17 Pages) Xicor Inc. – Secure SerialFlash | |||
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X76F128
ACK Polling
Once a stop condition is issued to indicate the end of the
hostâs write sequence, the X76F128 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 X76F128 is still busy with the
nonvolatile write operation, it will issue a âno-ACKâ in
response. If the nonvolatile write operation has
completed, an âACKâ 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
7052 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 X76F128
requires the master to perform an ACK polling with the
speciï¬c 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
ï¬ow.
Password ACK Polling Sequence
PASSWORD LOAD
COMPLETED
ENTER ACK POLLING
ISSUE START
ISSUE
PASSWORD
ACK COMMAND
ACK
NO
RETURNED?
YES
PROCEED
7052 FM 09
If the password that was inserted was correct, then an
âACKâ 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 âno
ACKâ 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.
Figure 5. Acknowledge Polling
SCL
SDA
8th clk.
of 8th
pwd. byte
âACKâ
clk
âACKâ
START
condition
6
8th
clk
8th bit
âACKâ
clk
ACK or
no ACK
7052 FM 10
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