WTB: Eprom Modules for the HP 75

[Sylvain Cote]

(10-05-2014 02:58 AM)Paul Berger (Canada) Wrote:  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.

Hello Paul,

You are right, there is two way of doing this, directly to the EPROM of through the 75 bus.

Option A: direct EPROM connection through a bed of nail
Advantage: easy to map it to a standard programmer
Disadvantages: not an easy task for a typical user, unglue/reglue the module, manage the connected components.

Like you said, I would have to manage the diode, the resistor and possible the hidden component on the side 2 of the PCB.
Since the PCB is a two layer, unsoldering the EPROM should give me access to the EPROM mapped pins in order to come up with the correct bed of nail. (PCB side 2)

Option B: through the 75 bus connector
Advantage: easy to reprogram for a typical user
Disadvantage: none really, except money and time for me ;-)

I would have to build a complete EPROM programmer (HW & SW) for the CMT-75-32KE.
I could take a arduino board with a AVR or ARM microcontroller (software: USB communication, HP-75 bus logic plus the GPIO lines)
connected to a custom daugther board that will handle the correct voltage and the lines mapping.

In both cases, I still need to convert the PMS generated file to an Intel Hex format for the EPROM programming.

If you have any suggestion or alternative please let me known, you are the expert here, not me.

Best regards,

Sylvain