Thanks for the responses, Steve. I'm suspicious about the lock bits on the D8751H's being set because reading back the devices after UV erasure shows mostly "00H"s with a few "1DH"s and "28H"s mixed in. In other words, the kind of gibberish you would expect to see if the lock bit was set (I had removed the 8751s from working circuit boards).

I posted the query because all the windowed EPROM micros I've seen in the past erase the lock bits along with the main array under UV. The post from 8-13-00 indicates this may not be the case for HMOS 8751s, and I was curious if anyone had access to the original AMD datasheet. The parts are kind of useless if the lock bit can't be reset, since a set lock bit prevents the part from running out of external memory (ie, it can't be used like an 8031). I'll probably just chuck the tube of parts and get some Atmel 89S52s.

The homemade programming adaptor works fine with an Intel CHMOS 8752BH, I'd be glad to share the details if anyone has a Needham's PB-10 they'd like to upgrade. The DOS programming software already handles 8751s, all you need to do is wire up an adaptor.