AMD 8751H lock bit

[laroche73]

OK, I did a search and came up with this response from from the 8052 forum on 8-13-00:

**broken link removed**

I also checked the original comment on the Philips archive. My question is, can anyone verify this? With every windowed EPROM micro I've dealt with in past, UV erases the lock bits as well as the main array .

Reason for the question: Last week, I modified an old Needham's PB-10 programmer to handle 8751/2s. For those of you who don't know, the PB-10 was a great ISA card programmer from the 80's that handles 2716s to 2Mb flash PROMs. Very nice design, but it's not currently supported. I scoped out all of the signals, identical to programming a 2764 except for the Vpp pin, which matches pin 1 for a 32 pin EPROM. I also have the right P.3 and P.2 pin levels.

From the original Intel databook, programming the 8751H looks like a subset of the 8752BH, aside from the 21V Vpp vs. 12.5V and the don't care levels on some P.2 pins.

The Intel 8752BH I have programs fine, encryption array, lock bits, etc. (went through the UV erase/program cycle a few times). The surplus D8751Hs I have don't read FFs, program, or patch, and I've erased them several times. Looks like the note mentioned above is correct, any further insights?

(Yes, I know there are better parts available, I'm just trying to put a tube of old parts to use in miscellaneous projects)

- Claude

 

[laroche73]

can't erase 8751H lock bit

After a little more searching through the old Philips 8051 archives, I found an answer, here it is in case someone else encounters a similar problem:

**broken link removed**

Another post elsewhere in the same archives made essentially the same comment. It appears that the lock bit on 8751's (windowed EPROM version) from certain vendors can't be erased once programmed. My experience agrees with this. With the Intel parts I can erase the lock bit and reprogram, not so on the AMD parts.