Per Erik's request, I have transfered this thread from another forum.

We have a board with the Intel 80C51FA(or B), clocked at 11.0592MHz. This has been in production over eight years. This board gets its operating code from another master board. This code is transfered as 32 1k chunks. A small bootloader is written into the slave board's Dual Port RAM from the master. The onboard processor is then released from reset to run this. The master sends one chunk at a time, which the local chip transfers to its code RAM. Eventually all the code is transfered, the local processor goes through another reset cycle, and comes up running the RAM code. Access times run around 360 nS. The -WR line is seen to run through out the process when writing to RAM. We only need PSEN and ALE to run the bootloader.

But not in the case of the P87C51M. Using an analyzer, this part never runs the -RD or -WR lines! There is never a sign of activity on an o-scope. Occasionally this part will start an aborted write cycle (-WR starts to go low), and then does nothing, it just hangs dead. Usually it goes through the motions of running the bootloader, with no write cycles to load the code RAM with, then switches to running out of the code RAM, which is random garbage at this point. Accesses are running around 180nS, which is to be expected. The engineer says we need only 95nS per access.

We switched to a faster PAL (from 15nS to 7nS) to decrease access times, but this didn't help. I connected Vcc to pin 23, which is a No Connect on the Intel part, to give it more power, but that didn't help. Studying the sheet doesn't readily suggest anything. A support email to Philips got a less-than-helpful response: use a different processor.

Has anyone successfully done this swap? Any pointers or tips? Has anyone else tried this and failed and would like to share what they tried so no one else has to repeat the same failing steps?

Thanks for your attention,
Kenneth Jennejohn
Gallup/Lantek