X76F200

5

followed by the new command code of 8 bits (1st byte of

the protocol.) If the X76F200 is still busy with the

nonvolatile write operation, 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 protocol.

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

X76F200 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 that was inserted was correct, then an

“ACK” will be returned once the nonvolatile cycle in

response to the passwrod ACK polling sequence is over.

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 pass-

word is incorrect until the 10ms write cycle time has

elapsed.

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 automatically 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.

Data ACK Polling Sequence

ACK

RETURNED

?

ISSUE NEW

COMMAND

CODE

WRITE SEQUENCE

COMPLETED

ENTER ACK POLLING

ISSUE START

NO

YES

PROCEED

Password ACK Polling Sequence

ACK

RETURNED

?

ISSUE

PASSWORD

ACK COMMAND

PASSWORD LOAD

COMPLETED

ENTER ACK POLLING

ISSUE START

NO

YES

PROCEED