Good Morning,

I have a problem which I believe may be associated with the psen line. On my board psen is not connected.

Last Friday I programmed an 87c52. It works fine.

Yesterday I programmed multiple chips, and they are not working. I can plug the "known working chip" into the board and it works fine.
I made no changes to the code within the chip.

When I place a scope and look at the pins, psen on the "known working chip is high"; however the not working chips I see an oscillation of about 2.45 Meg.

There is no external program memory or connections to psen.

Any ideas?

thank you.