Thanks for the many speedy replys.

Yes, it is a Philips part in a PLCC44 package. I don't have the exact part number at hand. Pin 23 is P4.0.

We are upgrading a board with an eight year history of running successfully. Better people than I have been up one side of this board and down the other. After an engineer tells me, the technician/aide, that the thing is running properly, I take it as gospel. Having said that, I can say I have seen every product with a processor running on it here screw up on power up occasionally. Cest Le Guerre (spelling?).

I have largely been ordered to obtain sample processors, plug them in, and report the results. I have also been ordered to obtain faster Intel parts (33MHz versions of the 80C51FA/orB) and 22.118 MHz crystals to investigate the possibility of plunking in a faster processor and tweaking counter variables. If the information is meager it is because I am not an engineer. I give you a clue as to what we're trying to use in the post title and mention the part we are presently using as an Intel 80C51F-something. I give you a generic description of the symptoms found in a quick check of various signals suggested by the engineer(s). Posting this info is largely my idea. I originally (laboriously) posted this to the Philips Microcontroller Discussion Group, where Erik said he wouldn't respond because he disliked the web service there, and said to post this here. So, here we are. If this seems like a lame shot in the dark, well, yeah it is. This is my idea to move things forward here until the engineers can sit down and grind through a stack of manuals and data sheets.

I think Jan's post gets to the heart of the problem. I have noticed a reference in the P87C51RA/B/C/D (the part recommended by Philips to replace the 87C51Mx mentioned in the title) sheets that an SFR bit has to be changed to force it into 6-clock/instruction mode. 12-clock-per is the power up default, which stays true to the Intel part.

And another, earlier thread on this chip suggests a bit had to change, but the responder couldn't remember the bit's name. So now I get to go the engineers and tell them this part has wierd memory layout issues, we have to rewrite code to get to outside RAM, and this is the bit...
This despite the fact that Philip really, really stresses how good this chip (the -M part) is for 80C51 substitution in their literature. The gloomy part is Philip's lack of notes on making this thing work in this situation. I have two phone numbers for tech support guys, but we never connect on the phone somehow. Their app notes give up nothing on this. And I now see that Philips is looking to sell off their semiconductor business. I don't think I can recommend these guys for future use...

I see this is a matter of grinding through hundreds of pages, learning the chip inside out, and applying all this to modified code. The circuitry is probably good to go. Or just going to a faster Intel part and faster crystal (and RAM, and PALs, and..)

Thanks again,
Ken Jennejohn