6.1 Counter Command

The Counter command reads or increments the count value of the monotonic counter. The counter value is stored in CSZ2. The maximum value of the counter is fixed at 10,000. The starting value of the counter is programmed during initial provisioning, and when the Configuration zone slot is locked, it cannot be modified.

The counter is designed to never lose counts even if the power is interrupted during the counting operation. In some power loss conditions, the counter may increment by a value of more than one.

The counter can be attached to either the ECC private key or to the HMAC key to limit its use. The counter will be incremented with the respective key until the counter reaches its maximum value, at which point the use of the key will no longer be permitted.

The number of legal uses for a key can be controlled by initializing the Counter to a nonzero value at configuration time. Contact Microchip for details.