Enhancing PETs and other Vintage Computers

[julie_m]

Foreword By Timbucus

This thread has arisen out of a tangent in a repair thread on repairing a Vintage PET:

https://www.vintage-radio.net/forum/...d.php?t=174829

The discussion swung to what people do once we have fixed them (do they even get used) and perhaps how we can make them more relevant and of increased use with modern projects that enhance without detracting from in many cases what are now museum pieces.


How about building a FrankenPET with a Raspberry Pi tucked inside it, obviously emulating disc drives but also generating a 256-shades-of-green display in time with the PET's pixel clock, and which can be overlaid on the PET's own screen?

By the way, I've just spotted you can generate things like NMI using [O]NMI[/O] .....

[SiriusHardware]

Seriously, on this forum you are suggesting substituting the real 1970 vintage innards of a vintage PET with a Raspberry Pi? Have a long hard think about what you've done.

I do believe someone does (or did) make a modern replacement, functionally identical PCB with all the right connecttions / connectors to fit inside original PETs where the original motherboard is a complete basket case, but we are a long way from that with this one.

Paul very kindly rustled up the 'overline' feature for that very purpose just a few days ago after I asked whether that feature existed. It didn't, but it does now.

[ScottishColin]

You mean you've done all this and never used a PET?

Wow. Just wow.

Colin.

[ScottishColin]

It helped start my career. I worked at Norwich Union/Aviva mostly before going contracting for a few years. Always in Infrastructure.

Did lots on mainframes and mid-range, lots of network stuff and big-time OS/2 support and development work for years before Windows killed OS/2.

Then moved to virtualization and strategy work. Retired now.

Colin.

Originally Posted by ajgriff

Lovely story and such a shame to have lost the original PET but I can understand why you're keen to get this one working. Definitely making progress now.

Alan

[SiriusHardware]

...never used a PET?

'Fraid not. When the machine finally gets back to the point where you can actually do things with it I won't be a lot of use, but no doubt it will all come flooding back to you and we have Slothie and Alan who do both have PETs, so you'll all be able to hang together and work all that stuff out between you.

I'm interested in old computers of all marques, especially in getting them working. A wise man among us (...not me) once said that getting old computers going is usually much more entertaining than using them once they do work.

[TonyDuell]

Originally Posted by SiriusHardware

[
I'm interested in old computers of all marques, especially in getting them working. A wise man among us (...not me) once said that getting old computers going is usually much more entertaining than using them once they do work.

Me? It's certainly a view I agree with. I've just spent a week sorting out a network bridge/router (early 1990s, ethernet is 10Mbits/second coax) with a 68000 processor in it, the interesting feature being there's a machine code monitor in the boot ROM. Now that it works, it's back on the shelf.

And not just computers. I'll spend time restoring a low-end tape recorder because I enjoy doing so, not because I need another thing to record sound.

[julie_m]

Originally Posted by SiriusHardware

Seriously, on this forum you are suggesting substituting the real 1970 vintage innards of a vintage PET with a Raspberry Pi? Have a long hard think about what you've done.

No, not substituting -- supplementing. The PET would be running Kernal, BASIC and whatever software you liked, perfectly as normal. The Pi would be listening to the IEE bus and doing whatever the real disc drive hardware would have done; either accurately timed or as fast as the PET would accept if only the spinning disc could keep up. It would also be listening in on the PET's display timing and generating its own video signal from a software frame buffer, perfectly in time with the PET's own pixels so as to allow overlaying by tapping (reversibly, of course) into the CRT drive signal. This is effectively "analogue", of course, even although the PET only ever drives it into one of two states; off or full on.

And who wouldn't have wanted a graphics co-processor as powerful as the mainframes of the day, if only such a thing had existed in the early 1980s? Modern parts obviously are not "authentic", but a modification can still be in keeping with the authentic spirit. Like a real-life reimagining of an artefact from a work of science fiction.

The enhanced graphics idea is a bit fanciful, for sure; but the disk drive emulation seems a reasonable proposition. It won't get in the way of existing software, because the PET can't tell the difference between it and a real disc drive; and all the work can be done in a way that is fully undoable, if the answer to What an I actually going to do with this thing once it's finished? turns out to be Bung it in the loft and forget all about it .....

Originally Posted by SiriusHardware

I do believe someone does (or did) make a modern replacement, functionally identical PCB with all the right connecttions / connectors to fit inside original PETs where the original motherboard is a complete basket case, but we are a long way from that with this one.

Definitely. A replacement motherboard would be very much a last resort. I'm sure there's enough of Colin's one working not to need anything as drastic!

Originally Posted by SiriusHardware

Paul very kindly rustled up the 'overline' feature for that very purpose just a few days ago after I asked whether that feature existed. It didn't, but it does now.

Ah, very nice! Thank you very much, Paul.

[Timbucus]

Originally Posted by julie_m

No, not substituting -- supplementing. The PET would be running Kernal, BASIC and whatever software you liked, perfectly as normal. The Pi would be listening to the IEE bus and doing whatever the real disc drive hardware would have done; either accurately timed or as fast as the PET would accept if only the spinning disc could keep up. It would also be listening in on the PET's display timing and generating its own video signal from a software frame buffer, perfectly in time with the PET's own pixels so as to allow overlaying by tapping (reversibly, of course) into the CRT drive signal. This is effectively "analogue", of course, even although the PET only ever drives it into one of two states; off or full on.

And who wouldn't have wanted a graphics co-processor as powerful as the mainframes of the day, if only such a thing had existed in the early 1980s? Modern parts obviously are not "authentic", but a modification can still be in keeping with the authentic spirit. Like a real-life reimagining of an artefact from a work of science fiction.

The enhanced graphics idea is a bit fanciful, for sure; but the disk drive emulation seems a reasonable proposition. It won't get in the way of existing software, because the PET can't tell the difference between it and a real disc drive; and all the work can be done in a way that is fully undoable, if the answer to What an I actually going to do with this thing once it's finished? turns out to be Bung it in the loft and forget all about it .....

Definitely. A replacement motherboard would be very much a last resort. I'm sure there's enough of Colin's one working not to need anything as drastic!

That use of the PI (a PI0 actually) was what ended up getting one included in the ZX Spectrum Next - with a Bare Metal OS it watched the actual video RAM for changes and rendered a frame on the HDMI - it was also fast enough to add some features like Sprites to make it easier for newcomers to get into programming. Now of course as the speed has risen all the system is included on the FPGA as custom graphics hardware and the PI has been repurposed with a Custom Diet PI Linux which acts to provide support for playing TZX preservation files that needs its oomph among other clever tricks.

A similar technology is used in the ZXHD an addon for old Spectrums which sells very well. Its big advantage for commercial use of course is every PI0 comes with a HDMI license.

I think I remember seeing something along the lines of using it to scan incoming video for a similar purpose but, can't lay my hands on the link at the moment.

Anyone interested in the original project can find the source for the bare metal OS here:

https://gitlab.com/victor.trucco/TK-Pie

I used a PET in the early 80's as a friend had one but, not since - I have always fancied one but, the sheer size and not going down the 6502 rabbit warren any further again than my large collection of C64 stuff means I do not give in (yet) - well OK I have my original BBC and I added an Acorn System 1 recently but, oh well sod it - that replacement PET you mention is here and it does look fun:

https://www.thefuturewas8bit.com/mini-pet.html

[julie_m]

Can one of the moderators please split this off into a separate thread? TIA.

[Timbucus]

Yes good idea thanks Julie - this could lead to some interesting discussion not just on the PET but, what can enhance a vintage machine after repair in a considerate way that encourages its continued use by the owner...

[Timbucus]

I am going to suggest a Split at Post 810 with a title "Enhancing and using our pets when they are fixed..." this will cover other machines as well if the discussion diverges slightly and leave the original thread clean for discussion on the repair?

Unless anyone objects I will create the Thread and PM CobaltBlue with that request.

[SiriusHardware]

If possible, keep 812-815 in this thread as they are clearly directly on this topic.

[Refugee]

I would go for enhancing vintage computers or pets and other vintage computers.

[SiriusHardware]

Someone enlighten me: What options are available as substitutes for the tape units and HDD units for Commodore computers?

Since the signal in / signal out to the tape units is essentially TTL-level data it strikes me that anything capable of generating or reading that data in the correct format (such as an Arduino) could be pressed into service for that purpose, in fact I would be amazed if it has not already been done with an Arduino or Raspberry Pi. You could potentially also use an Arduino to generate test data to send to one of the cassette units.

What about substitute HDD units - did the PET ever support an HDD such as the 1541 which was used with e.g. Commodore 64? How did the computer communicate with that?

[Timbucus]

I have not seen anything in my browsing to indicate PET replacement cassette decks.

I think most people in the commodore world go for the SD2IEC which is also available for the PET

https://www.thefuturewas8bit.com/sd2pet-future.html

they emulate Disk drives in an amazing fashion I have one for my C64 which works fine with my full size Disk drive to copy files to and from real disks.

[Slothie]

There is a device called SD2PET that connects to the IEEE-488 interface and uses SD cards to simulate various Commodore disk drives. https://www.thefuturewas8bit.com/sd2pet-future.html
There were a number of commodore disk drive units for the pet, the 2040, 3040, 4040 etc. They were all dual-floppy units with their own dual 6502-cpu controller built in. You could even upload code to the controller and execute it...

There are also devices that allow "TAP" files to be saved onto SD cards and played back/recorded in a similar fashion - most of these are aimed at the C64 but many will work with the PET. For example, the "Tapuino" and various Pi projects: https://diyhacker.com/raspberry-pi-c...-tape-emulator

[SiriusHardware]

My memory of the 1541 - a friend had one for his C64 - was that it was astoundingly slow. How did that connect to the computer, through an IEE-488 interface or by some kind of serial connection, or direct to the buses like Sinclair ZX interfaces?

I have something called an 'Ultrasatan' (Don't ask me why that name) which makes an SD card 'look' like an original Atari HDD unit to an Atari ST computer. I bought it when one of the GALs in the AdScsi interface in my ST HDD died - fortunately the content of the SCSI drive itself was OK so I connected it to a SCSI card in a Linux PC, imaged the HDD content (all 60MB of it) to a file and then copied that image onto an SD card and to as many other places I could think of while I was at it - a great relief, as there was a lot of stuff on the original HDD which I would not have wanted to lose. My STs, one of them my original machine from 1986, are still regularly used.

I've also got a 'Vdrive ZX' which is an electronic substitute for the innards of a ZX Microdrive - uses SD cards as the storage medium instead of those horribly flaky microdrive cartridges. (Tim put me onto that one).

What constantly surprises me is that there is still so much love for these old machines that people still sit beavering away on useful hardware projects and even brand new software, a phenomenon which, far from declining, seems to have actually increased in recent years along with supplies of parts and replica PCBs which were not previously available.

[Timbucus]

Yes it was incredibly slow - I cant remember the details but, it is due to some design flaw that the serial bus it is connected through (a sort of IEE488 on five pin DIN sockets) is slowed down. You can get several speed up cartridges which load custom firmware into the 6502 processor on the disk drive (yes it has its own CPU) to make it usable. I obviously use one...

https://vintageisthenewold.com/sd2ie...stcart-review/

Out of interest last year I bought a 1541 interface for my ZX81... - I have one for my PC as well...

I never had a HDD for my (also original) Atari but, I certainly used it a lot and have 100s of floppies... I will look into the Satan. My ST went (with its Mono Monitor - sadly lost to time) into my first wage slave job as they had practically no computers and I needed a wordprocessor and spreadsheet to undertake the fairly large project I had been given. Early BYOD!

Yes the VDrive is amazing - you can get a small add on for it now as well that has a recording of the noise that the carts make so it sounds authentic as well The range of addon SD devices, sound cards from multiple suppliers is astounding.

As you probably know I have been able to get PCB's for MK14 (3 types and we know of more), Acorn System 1 (Two suppliers as far as I know), Triton (Two working replica PCB makers and two in development enhanced respins), SCRUMPI1 (of course - the 3 is not forgotten and making slow progress) and I have heard a whisper of a System68 one. You can of course get Altair, IMSAI, PDP clones etc and there are a lot of people who build Apple1 - I have a PONG board on the way - yes I know... project list length overload.

In terms of addons the list is never ending with stuff for every machine you can imagine including Amiga's that browse the internet - I only have a USB replacement onboard floppy drive for mine.

There is even an active clone and addon community for QL's.

My Dragon 32 has a replica of an 1980's 80 column card and a of a similar lower case addon. You can get two different SD card systems for them - one from the extensive CoCo community.

I have an SD card system for my Oric and ATMOS...

So as you say even the more obscure systems are thriving... and growing. I think the Spectrum Next group is one of the largest (retro) on facebook with 9.4K members...

[Slothie]

The commodore 64 drive interface was serial using a protocol based on the ieee-488 paralell bus protocol. It was slow, about 400 bytes/second without fastloader software and significantly slower than the Atari floppy drives that were also connected by a serial bus. With fastloader software it was a more respectable 2.5kbytes/s.

[ortek_service]

Regarding the Commodore 1541 Floppy Disk Drive, it's fairly well known that the Commodore Engineers did a rather late software bodge to make it work, after an issue with an IC feature they were relying-upon to resolve speed-issue with previous original VIC-Only 1540 drive which they'd been forced to maintain compatibility (that was first to use the new Commodore Serial-only IEEE-488 bus, and also had speed-issue)
http://www.zimmers.net/cbmpics/d1540s.html

The 1541 last-minute software fix apparently resulted in only one sector being read per disk-revoluton rather than the whole track of sectors. With some explanation here: https://en.wikipedia.org/wiki/Commodore_1541


The original PET drives, with the standard full IEEE-488 connector were actually much faster as they didn't have this issue - that was only on the drives with the cut-down Serial-only IEEE-488 DIN connector for the VIC-20 / C64, and that cassettes could actually be faster (especially with Turbo coders). Although there was also some later 3rd party turbo upgrades for the 1541.

There's quite a lot of summary of specifications for all the different Commodore drives, here: http://www.6502.org/users/andre/peti...drive_info.txt
- But not sure if they've confused kb/s with KB/s, as otherwise the 1541 is only 400bits/sec, rather than 400Bytes/sec mentioned in previous post. But that could well be the case, if it was slower than cassettes, as these seem to be around 400bps effective speed, due to 800baud rate being effectively halved:
https://www.lemon64.com/forum/viewtopic.php?t=54041


BTW, it appears in an earlier post that HDD was mistakenly referred to instead of FDD (especially with reference to the 1541). I don't recall there ever being an official HDD for the C64 / especially the VIC-20, as the cost of HDD was as much as a fairly-new small car back then. However, it seems there was a (rather rare, ) PET one: https://en.wikipedia.org/wiki/Commodore_D9060
And it may have been able to use an equally-expensive generic IEEE-488 storage device, with suitable software support.


For the Commodores, there are some rather lower-cost alternatives these days, like the Pi1541 board which converts an RPi into an emulator of the 1541: https://cbm-pi1541.firebaseapp.com/


And also the Tapuino C64 C2N / 1530 Tape Emulator PCB, which plugs onto that interface has an ATMega328 (Arduino) uC + mini OLED display + MicroSD card and allows you to load /save .TAP files
https://www.c64-wiki.com/wiki/Tapuino_C64
https://easyeda.com/wagiminator/c64-tapuino-smd


There's lots of earlier ones listed here (but doesn't have Pi1541):
https://en.wikipedia.org/wiki/Commod...tape_emulation