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X76F640WE Datasheet(PDF) 6 Page - IC MICROSYSTEMS |
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X76F640WE Datasheet(HTML) 6 Page - IC MICROSYSTEMS |
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6 / 17 page  X76F640 6 ACK Polling Once a stop condition is issued to indicate the end of the host’s write sequence, the X76F640 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 X76F640 is still busy with the nonvolatile write operation, it will issue a “no-A CK” 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 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 X76F640 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 NO YES PROCEED 7025 FM 08 Password ACK Polling Sequence ACK RETURNED ? ISSUE PASSWORD ACK COMMAND PASSWORD LOAD COMPLETED ENTER ACK POLLING ISSUE START NO YES PROCEED 7025 FM 09 |
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