Hi Jay,

I used a pattern up to all 128 bytes without success.
Means, it was not destroyed during power off up to minutes.

But I use it still to detect a return from power down mode:
All normal program execution destroy this variables.
And only before power down was entered, the right pattern was written.

E.g. this was used in my clock:
http://www.specs.de/~danni/ap...hr4536.htm


Hi Alex,

another idea:
Add a capacitor (100nF) on a P0 pin against VCC.
So after power on reset this pin was read as 1.
And after this, put the pin to 0. This would charge the capacitor.
So on any further (manual) reset the capacitor was already charged and the pin was read as 0. Since no pull ups on P0, the capacitor was only discharged during power off (with internal clamping diodes of the 8051).
Naturally this pin can no longer be used to access external RAM / ROM.


Peter