Dear Michael!

The blown pin is a mystery. There is no error in the schematic - it is verified by several other engineers - I drive two 74HCT gates to select between the 32K RAM, the 32K PEPROM and Outport-Latch.
The Prototypboard is working fine since weeks, I have measured very accurately, there is no short, no wrong connection, no component which could produce a high-voltage-peek.
The pin blow after I have programmed in a new software, the software is quite simple, it jumps just to the external ROM at 8000H - there is
the main program located.
I have written tens of different programs, which were located in the internal CODE Memory of the chip - and they worked fine, also on the Prototypboard. But I have never executed addresses higher than 8000H.
I could see the pin worked fine under these other software: It kept high as default and got low at every RAM access.
I can't imagine, that software can blow the hardware, could it?
But I can't find a hardwareproblem as well.
It is just a mystery - not even my experienced colleques arround have any glue what it could have been.
I have drawn the schematic in Visio5 and forwarded it to your email-address.

Thanks for your answer!

Regards

Andreas Schweinzer
Electronic Systems Laboratory, Stellenbosch, SA