First time powerup (virgin) recognition question

Hi All,

I am using the Renesas RL78 G23 microcontroller.

I want to be able to identify a first time power up (aka virgin power up). I was thinking I could write a signature value to some register that can't be erased. I can’t use data flash or code flash because those can be erased (accidentally or on purpose).

Do you know of something like this?

To recap –

• The unit wakes up for the absolute first time
• It is recognized that it is the first time (because the special register or equivalent has not been set)
• Write special value
• Any time we power up after that we know it is a non-virgin power-up because the special value is there.
• Once the special value is written, it is important that it can never be erased for the lifetime of the unit.

Anyone have ideas on how to do this?