HP-71B DIY RAM Modules anyone?



#11

being a HP calc user ever since 1982, i started to focus on refurbishing in the late nineties; the differentiation between a "refurbisher" and a "collector" simply being the former putting the freshly acquired items on the shelf and the latter putting them on a display.

i have been quite happy so far with just fixing broken posts, displays, kinks and scratches, until recently, when somebody here on the forum came up with the question of what machine to be preferably used for doing matrix math.
iirc, valentin put some salt directly into the wound of the sheer HP-71B ignorance in this forum, and, yes, digging through the rubble on the shelf, an HP-71B came to light.
inserting fresh batteries and reading the fine manuals was a two night's job with the lust for more. but, alas...
just 4k of extra memory aren't something what i would call an appetizer.
so, here goes:
the idea is to get some low power 32k x 8 CMOS SRAM bolted to a PIC18Fxxxx (that would simulate the ILQ4) and make a nice 32KB memory module for the HP-71B out of it.

Has it been done before? any comments on feasibility?
(may the inclined reader bear in mind that the author of these questions is well seasoned in handling kilovolts and kiloamps, but may fail with kilobytes)
cheers,

hans


#12

Hi,

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.

Diego.


#13

I am definitely interested in expanding my HP-71B. I have asked myself recently if using the processor of a HP-48 inside the HP-71B would not be an easy way to do this (copying the OS on PROMs and using commodity SRAMs). However, interfacing to the keyboard and display seems to be a problem with that approach.

A NoVRAM-71 would be very interesting ... I wouldn't mind soldering the components directly into the HP-71 (or the card-reader slot), since the module shells are so scarce.

#14

Hello All

...

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.

...

There seems to be that the description of the bus info is available in the HP71 Hardware Internal Design Specification available here.



Regards,

Chris





Edited: 13 Nov 2007, 4:03 p.m.


#15

Hi,

Oops!! Thanks Chris, yeah, this info is actually in the MoHPC DVD right on my shelf... Indeed the only missing info in the HP-71 HW IDS vol.3 are some pages from chapter 8 (schematics) that I got elsewhere some time ago.

Still the rest of considerations remain *active* though.

- Module shells difficult to find.

- Connectors *very* difficult to build.

- Tight code timing (71's clock more than doubles 41's) so chances are that PIC's are not suitable for that particular application.

- Etc, etc...

But, if it was easy it wouldn't be funny!! ;-)

I still have to achieve a couple of improvements on my previous projects: The NoV's Auto-OFF bug on CX's and the new NoV-64 during '08.

NoV-71 could be a nice project for the rest of the year. Or at least I can learn a lot about 71's internals :-)

Thanks again and best wishes.

Diego.


#16

Hi,

I would be interested in a completely different thing,

more exactly using an HP-71B HP-IL module with an HP-48...

...now _that_ would be a challenge;-)

Regards

Raymond

#17

hi diego,

thank you for your kind response.
in general, i do agree with you, however...

Quote:
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)

if this is going to be team project of forum members, i'll be taking care of that. so, consider the problem of enclosure shortage as being solved.

Quote:
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.

heck! that stuff *is* flimsy! i am currently looking for an alternative. stay tuned.

Quote:
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)

i did it. some bloodshed, but still alive and kicking. module itself survived surgery in very good shape. however, that's truly something one would not do twice without desperate need.

for the documentation, the IDS gives a good starting point.

using the card reader bay or adding the extra RAM internally is simply out of question (for me, that is); the idea behind is leaving the HP-71B unmodified as far as possible.

for the "floorplanning":

the internal p.c.b. of the 4k module is 19.9 mm x 23.5 mm. board thickness is 0.8 mm, while the height of the internal stand-offs is 3 mm (which limits the maximum height on the component side of the p.c.b.)

hope, that helps...

best regards,
hans


#18

Quote:
using the card reader bay or adding the extra RAM internally is simply out of question (for me, that is); the idea behind is leaving the HP-71B unmodified as far as possible.

Who said anything about modification? It would just plug in.


#19

best regards,
hans


#20

Well, I guess I don't understand your point. To me, plugging a newly designed memory module onto the connector pings in the card reader compartment isn't "modifying" anything.


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