The Run-Time clock is given in milliseconds and days. Both are 32-bit numbers. This value is saved in nonvolatile memory whenever a STORE_DEFAULT_ALL command is issued. It can also be saved when a power-down condition is detected (See Section 7.4.19).

The Run-Time clock may also be written. This allows the clock to be periodically corrected by the host. It also allows the clock to be initialized to the actual, absolute time in years (e.g., March 23, 2010). The user must translate the absolute time to days and milliseconds.

The three usage scenarios for the Run-Time Clock are:

1. Time from restart (reset or power-on) – the Run-Time Clock starts from 0 each time a restart occurs
2. Absolute run-time, or operating time – the Run-Time Clock is preserved across restarts, so you can keep up with the total time that the device has been in operation (Note: “Boot time” is not part of this. Only normal operation time is captured here.)
3. Local time – an external processor sets the Run-Time Clock to real-world time each time the device is restarted.

The Run-Time clock value is used to timestamp any faults that are logged.