WTB: Eprom Modules for the HP 75

[Paul Berger (Canada)]

(10-05-2014 02:32 AM)Sylvain Cote Wrote:  

(10-04-2014 02:35 PM)Michael Fehlhammer Wrote:  I don't have a special eprom burner, but since I've read that CMT used standard eproms (27C256) I might be able to burn an eprom outside the module, using a standard eprom programmer.

Hello Michael

This link point to the CMT flyer for their EPROM modules
https://db.tt/UdfstGeg

The following pictures shows the CMT-75-32KE modules complete and taken apart
https://db.tt/KKisinJB
https://db.tt/rTW1HBjL
https://db.tt/yuNOnyVy
https://db.tt/0Z8PnzpW

This link point to the Microchip technical Reference Document for the 27C256 EPROM.
https://db.tt/WSVBPjUw

The CMT module uses the 27C256 EPROM with the PLCC package format directly soldered on the PCB.

Two solutions exist to reprogram the chip ...
1) unsoldered the chip from the board and put it into a an standard EPROM programmer with the PLCC adapter on it.
2) create a special PCB EPROM programmer adapter that map the connector and the three additional pins

In both case we also need to understand the PMS file structure to extract the 32K image needed for burning.
I have a PMS with the softwares and manual for it.

I have started 2 years ago a project to do the special PCB (option 2) and the extraction software, but never got around to finish it.
At some point I will finish that project, maybe in 2015.

Best regards,

Sylvain

For option 2 do you mean the connector that plugs into the 75? or the pads under the EPROM? If you mean the the connector that plugs into the 75 you would need to emulate the 75 bus to be able to present address and data to the EPROM. Fortunately the 75 bus is not complicated but address and data are clocked out in 3 sequential bytes so that would rule out just mapping over the pins. The one I have does not have the 3 pin connector or the diode on the top side but there are a couple solder bridge connection that pull up the Vpp line that would need to be cleared.