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Eprom Modules for the HP 75
10-06-2014, 02:52 AM
Post: #2
RE: Eprom Modules for the HP 75
(10-05-2014 07:15 PM)Sylvain Cote Wrote:  
(10-05-2014 05:10 PM)Michael Fehlhammer Wrote:  Should we move, or should I post a reference to that thread in the general forum?
That is a good idea, it will be a better place than here.

(10-05-2014 05:10 PM)Michael Fehlhammer Wrote:  I dream of a collection of HP -75 tool set like the JPC rom for the HP 71b.
Same here. 8-)

(10-05-2014 05:10 PM)Michael Fehlhammer Wrote:  Even if we had a programmer adapter or specialized eprom programmer, we still lack a source of eprom modules, they seem to be extremely rare.
Or can you imagine a way of producing them, including the module housings ?
Could rom modules be modified to become eprom modules?
( But since even the most common HP 75 roms are relatively rare and expensive, that wouldn't help that much ).
This means that I would have to create something like Diego did with it's Clonix-D/NoV-64 modules for HP-41.

If we go that route, then we need to do the following ...
- Choose a microcontroller to do the 8/16/24/32KB module simulation
- Make a prototype, test the electrical consumption and the impact it has on the HP-75 OS.
- Find a connector that is compatible with the motherboard socket
- Design/produce/assemble the PCB and it's components
- Come up with something to help push/pull the module inside and keep it in place.
--> a traditional mould for the housing would be way too much expensive.
--> a 3D print module housing (I would need to experiment on the plastic push/pull resistance of such a module)

Such a project is feasible, but currently I do not have the time to do it.

I have put on dropbox the following zip file for the PMS

82713A Plug-In Module Simulator [manual+soft] (sc).zip

The 65MB zip file contains ...
82713A Plug-In Module Simulator [manual 150dpi ledger] (sc).pdf
82713A Plug-In Module Simulator [manual 150dpi letter] (sc).pdf
82713A Plug-In Module Simulator [manual 300dpi ledger] (sc).pdf
82713A Plug-In Module Simulator [manual 300dpi letter] (sc).pdf
82713A Plug-In Module Simulator [soft cards] (sc).pdf
82713A Plug-In Module Simulator [soft catalog] (sc).txt
82713A Plug-In Module Simulator [soft tape] (sc).dat

Best regards,


Finding a compatible connector will be a big issue, the pitch for the connector is very odd and I have never seen any like it. A gentleman I correspond with has a tool for measuring connectors and he says the pitch is 0.109 inches, it is just far enough off of the common 0.1 inch pitch be be a problem. The other issue is the boards in the 75 are made of quite thin fibreglass board stock. I just ran into this trying to find an edge connector to plug one of the 8K modules onto (it is 0.1 inch pitch) but any boards I had here where two thick, so i ended up hacking the connector off of a junk 75 board I have here that from a 75 that had suffered the worst battery leak I have ever seen. This will be my source of edge connectors to make my connection to the EPROM as well.

Later this week I should get around to trying to see if I can talk to the EPROM outside of the 75, I finally figured out how the get data in and out of the DIO cards in my 9000-310 and I have it set up right now to test a memory module, when I am done with that I will give the EPROM a try.

In one of your posts you mention a bed of nails connection to the EPROM, well the one I have the pads on the bottom next to the connector and on the outside edge are very tiny and would make getting a reliable connection difficult. There should be a pad on the bottom that corresponds to each active pin on the EPROM.

My ideas for enhancement to 75 are:
  1. Build a non-volatile PMS, this should be pretty easy just replace the SRAM memory with FRAM. FRAM is non-volatile and you can read and write it just like RAM and is plenty fast enough to keep up with a 75 and also replace the discrete logic with a CPLD and fit the works into an expansion POD.
  2. Convert the RAM disk in the expansion POD to use non-volatile FRAM memory so contents would be preserved even if the the batteries go dead, it may be even possible to expand the size of it but that would require some coding.

I have considered making things that will plug into the front but that odd pitched connector makes it difficult.
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RE: Eprom Modules for the HP 75 - Paul Berger (Canada) - 10-06-2014 02:52 AM

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