X76F128HE datasheet(6/17 Pages) XICOR

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X76F128

ACK Polling

Once a stop condition is issued to indicate the end of the

host’s 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 “no-ACK” in

response.

the

nonvolatile

write

operation

has

completed, an “ACK” will be returned and the host can

then proceed with the rest of the protocol.

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

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.

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.

Data ACK Polling Sequence

ACK

RETURNED

ISSUE NEW

COMMAND

CODE

WRITE SEQUENCE

COMPLETED

ENTER ACK POLLING

ISSUE START

YES

PROCEED

7052 FM 08

Password ACK Polling Sequence

ACK

RETURNED

ISSUE

PASSWORD

ACK COMMAND

PASSWORD LOAD

COMPLETED

ENTER ACK POLLING

ISSUE START

YES

PROCEED

7052 FM 09

Figure 5. Acknowledge Polling

8th clk.

of 8th

pwd. byte

‘ACK’

clk

8th

clk

‘ACK’

clk

‘ACK’

START

condition

8th bit

ACK or

no ACK

SCL

SDA

7052 FM 10

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