HP Portable Plus (Model 45711) - home-brew expansion drawers?

[clueless_engineer (Brett)]

Hello,

I have a model 45711B that includes 128KB of base system RAM with an additional 128KB of expansion RAM via a 82981A memory drawer.

Was wondering if anyone knew of home-brew versions of the 1MB expansion (82992A) and/or ROM expansion drawer (82982A)?

There are schematics available in the service manual so might have a crack at it myself ... if someone more qualified hasn't done this.

I have a video pulling mine apart here (if interested).

Brett.

 

[clueless_engineer (Brett)]

Actually, it seems that my 829812 memory drawer (128KB) contains two 82984 daughter boards (128KB each), so it's actually a 384KB memory expansion.

 

[Martin Hepperle]

HP also provided a 1 MB RAM drawer 82992A (see https://hpmuseum.net/display_item.php?hw=925)and some 3rd party companies offered, as far as I know, up to 4 MB drawers. A very good source of information was/is Hal Goldsteins Portable Paper.
I am not aware of any published home-brew RAM expansions.

It would make a useful project to design a drawer with modern chips, maxxing out the capacity of a RAM disk and minimizing power consumption..

Martin

 

[clueless_engineer (Brett)]

Hey Martin!

Oh, of course, the Portable Papers ... good idea, they might have some projects in there. Will check them out.

Not sure if the ROMs have been dumped, but I created a Github repository with them. And I'll probably have a crack at drawing the 1MB schematic into Kicad as a starting point.

I know the max. usable system RAM is 512KB and anything over that is allocated to the RAM disks, so that would be good to max them out.

Brett.

 

[Martin Hepperle]

The Portable paper does not have much about hardware details or projects (except for a RAM expansion of the initial HP 110 (not Portable Plus)), but 3rd party products were advertized, including RAM drawers.
The magazine has some very useful programming examples for screen or HP-IL access, though. Turbo Pascal 3.02 can also be installed with an EPROM.
Yes, for MS-DOS 512 KB can be considered sufficient. But having a large RAM disk of, say 4-8MB would be very useful, if you want to compile programs or load larger development environments like a "C" compiler. Then you would not need an external disk drive.

I am not sure what the firmware limit of the RAM disk would be - if the ROM system is too limited, one could always resort to an installable device dreiver.
The Technical Reference Manual is on bitsavers - it also describes the interface to the drawers.

Martin

 

[clueless_engineer (Brett)]

Thank you Sir!

That Tech Ref Manual is really good, thanks! I was going to just get a 12VAC plug pack and use that as the charger (once I got my hands on a new battery), but I see the TRM says it needs to be current-limited, and also gives a simple design for a car charger ... so I might be better off just using my bench supply (with current limiting) as the re-charger.

Do you know if any dumps of the ROMs (1-2-3, Turbo Pascal, etc.) have been made? I'd need to get my hands on a ROM software drawer first.

BTW, I booted it up last night (just ran some wires from my bench supply to the battery terminals) ... working very nicely ... a mere 90mA @ 6VDC. The default configuration for the 512KB of RAM I have is 80KB for system and 432KB for the RAM disks.

I love it. Quite a simple, well put-together machine.

Brett.

 

[clueless_engineer (Brett)]

I do have the correct plug for the recharger port (from a Euro calculator power supply I think), but I see another option could be to install a 2.1mm DC socket where the internal modem's RJ11/12 socket would be (to the right of the DE9 socket). This would allow a standard 2.1mm plug to be used for the charger (remembering the current-limiting requirement).

Brett.

 

[Martin Hepperle]

For additional information and some EPROM images you might also want to look at Jeff's web pages.

An (EP)ROM drawer should be installed in your machine - usually the system came with one RAM and one ROM drawer.

PS: The operating system supports up to 2 MB of RAM disk plus the 512 KB of main RAM.
Using more RAM-Disk space would then require a MS-DOS device driver which control I/O to the RAM disk.

The original lead batteries prefer a small constant charging current ("trickle charge") and not being fully discharged.
One should already recharge when the indicator says 70-80% of charge (no full cycling like on NiCd cells).

If course, today, one could also build a new battery pack with Lithium Polymer cells and suitable charging circuits and regulator for 6V output.

And of course, with your setup: do not reverse polarity ... yellow/yellow banana plugs may be risky ;-)

 

[Brian Todd]

For additional information and some EPROM images you might also want to look at Jeff's web pages.

An (EP)ROM drawer should be installed in your machine - usually the system came with one RAM and one ROM drawer.

Interestingly enough Brett's unit has a RAM drawer and what looks like a blank for the ROM drawer. I have an "F" unit (512 massive KBs built in ) which has the ROM drawer but only a blank for the RAM drawer. My point being that the drawers were possibly optional at the time?

PS: The operating system supports up to 2 MB of RAM disk plus the 512 KB of main RAM.
Using more RAM-Disk space would then require a MS-DOS device driver which control I/O to the RAM disk.

The original lead batteries prefer a small constant charging current ("trickle charge") and not being fully discharged.
One should already recharge when the indicator says 70-80% of charge (no full cycling like on NiCd cells).

If course, today, one could also build a new battery pack with Lithium Polymer cells and suitable charging circuits and regulator for 6V output.

I rebuilt the battery of my Portable Plus by using an identically sized 6V battery and by splicing on the strips from the original. Curiously enough my Portable 110 has the three Gates cells instead of the Panasonic battery ... wonder whether these were once interchangeable?

And of course, with your setup: do not reverse polarity ... yellow/yellow banana plugs may be risky ;-)

@Brett - love your YouTube video of the teardown .. I never completely dismantled mine so interesting to see it's guts!