|Re: HP-71B DIY RAM Modules anyone?|
Message #2 Posted by Diego Diaz on 12 Nov 2007, 10:00 p.m.,
in response to message #1 by Hans Brueggemann
Certainly feasible, not for the average DIY guy though... :-)
In terms of design, there will be differences between the (suggested name) NoVRAM-71 and its HP-41 counterparts (Clonix, NoVRAM's etc.). But the overall concept is quite similar.
One main issue regarding the HP-71 is the lack of enclosures to build the modules. (There are far less 4K 82420A modules around than the ubiquous 82106A and I'm finding dificulties in obtaining the latter) Further more, the connector inside the HP-71 modules is not a separate part but a set of 13 flat "wires" directly welded to the PCB and tightly aligned together at 0.05" pitch. Not and easy task if you plan to solder them by hand. Add to this that opening an 82420A module is not a trivial task... (if you want to have a re-usable enclosure at the end of the process)
There is still another issue, that migth be overcome: I've find no hardware technical info regarding HP-71 I/O bus signals and timing, just the schematics diagrams. But this info is probably available somewere else.
Another approach would be gaining access to the internal bus through the card reader port (11 pins in a row at 0.15" pitch)...
As usual I'm almost obsessive regardig RAM volatility, so the use of a 256Kbit non-volatile RAM will become mandatory.
Mmm... well, let's think of it... :-)
Best wishes from the Canaries.