Knowledge Base

Permament memory allows just 13 bytes of RAM (data memory) to be saved into a non-volatile memory as a indivisible (all or nothing) block to be later restored. The two instructions for this are PermStore and PermRecall.  The 13 bytes of RAM are at address 6 thru 18 inclusive.

What makes this type of memory special compared to the other types of NVEM is it knows if the data being recalled is valid.  This means PermRecall can tell you if:

  • There is nothing to recall (you’ve never written to it).
  • Recall was successful.
  • The previous version of data was recalled (this may occur if power failed during a PermStore).

Writing to permament memory typically only takes a few milliseconds but it can sometimes be quite slow, taking up to 100ms.  During this time your control application will be stalled, so ensure your machine is in a safe state before performing a PermStore.

Permament memory endurance on the HMI430/700 is greater than 2.5 million writes.  There is no limit to the number of reads.