#pc-xt — Public Fediverse posts

PDS – the Programmers Development System – Part 2

This series of posts looks at the Programmers Development System (PDS).

• Part 1 – Introduction, background and some initial reverse engineering.
• Part 2 – A closer look at the PC ISA Interface card.

Having now got a bit of an idea of how the PDS appears to work in my previous post (PDS – the Programmers Development System) I’m now taking another look at the PC interface and starting to think about the possibility of recreating the system.

The PC Interface

Having decided I couldn’t rely on the schematic on the CPC wiki, I’ve taken the printout-versions of the PCB traces and started tracing them through to see what is really going on. It was greatly helped by the PCB view that can be found here: https://lemmings.info/pds-programmers-development-system/

Of course, I am assuming here that the remade PC card does actually work.

It turns out the ISA to Intel 8255 part was fine, including the address decoding, but the three 8255 IO ports, through the octal line buffers, to the two PDS links are fundamentally missing some key links.

Essentially the three 74LS244s are configured for half in A->Y form and half in Y->A. The three IO ports (PORT A, B, C) are also split in half. This means that most of this circuit is working in 4-bit chunks.

The high level linkages are shown below.

So here we can see how the A halves of each of the 244s handles OUTPUT and the B halves handle INPUT. We can also see that U5 (sticking with the original schematic numbering for now) handles the control signals, U4 is D4-7 and U3 is D0-3. PORTC drives U5 and thus also handles all control signals.

We can also see that the data lines are now fully bidirectionally connected so that each can be connected to an OUTPUT or an INPUT depending on the state of the PC2 line. PORTB handles the OUTPUT and PORTA is the input.

The control signals are still mirrored as determined in the first part, but now we can see that some are OUTPUTs and some are INPUTs. The mappings from PC0-7 through to the link pins is shown below (note I’ve reverted to using the same PDS connector pin numbers as the ZX Spectrum schematic in the diagram above and table below).

There are two swapped pairs of connections, two common, and one unique to each.

As mentioned previously, the ZX Spectrum interface does not connect to pins 9,11,13,15 so that implies to me that it would not work out of link 2 without remapping in the software for the alternative pinout.

From working through the ZX Spectrum monitor code in part 1, we can infer the following functions:

• Pin 3 (OUT): PC to Target CLOCK
• Pin 5 (IN): Target to PC CLOCK/ACK

We can also note the following:

• Pin 11 (OUT): Direction based on PC2. HIGH = PC to Target; LOW = Target to PC

From this point I can now fully recreate the schematic and start to think about recreating the PCB.

The PC Hardware

One slight sticking point in remaking the PCB was getting useful dimensions for an XT era ISA card. Two useful references I found were:

• The ISA Spec can be found as part of the PC XT Technical Reference: https://bitsavers.org/pdf/ibm/pc/xt/6361459_PC_XT_Technical_Reference_Apr84.pdf
• Researched 8-bit ISA card dimensions: https://www.andavno.com/?p=87

The actual spec wasn’t massively useful to me. I don’t know if the ends of cards was slightly different in PC XT systems, but it doesn’t seem to match the photos of the PDS PC card. The second link was very well researched and complete however, so I went with that.

One compromise though was trying to keep the card within a 100x100mm footprint, so I’ve not extended completely to what I believe will be long enough to have an end plate.

The Schematic

The updated schematic is shown above. I’ve added a few things I’d expect to see on a modern design – additional 100nF capacitors (one for each IC), and a resistor network to pull up all unused inputs to the 74LS04.

I originally went with the ZX Spectrum version of the 16-way connector, but then when it came to assigning footprints, to get a right-angled IDC connector meant pin one was now in the wrong place, so I had to revert to the alternative pin numbering as per the original schematic.

The PCB

I’ve followed the original layout used on the PC card remake as far as possible, reasoning that the person who did this almost certainly knows a lot more about electronics than I do.

One thing I wasn’t sure about was a GND fill. I initially created a fill zone, but then decided I’d follow the original lead and use explicit GND connections. If someone advises that a fill will be better then it is pretty trivial to add in.

Other points to note:

• A already mentioned I’ve kept this within the 100x100mm footprint. This leaves two unknowns: will it be tall enough to be useful; and will it extend to the edge of a PC case?
• The two connectors extend beyond the edge of the PCB, so they hopefully will be available at the edge of a PC.
• The dimensions are such that more of the PCB is off to the right compared to the photos of the remade board I’ve seen.

This will do for now, but I think it is highly likely there will need to be some physical adjustments for this to be usable.

Conclusion

I believe I’ve got an accurate schematic for the board based on the photos available and I now have design for a candidate PCB. The problem is that I don’t know anything about what the software is expecting when it drives the Intel 8255 to work the PDS interface.

There is also the small matter of needing an ISA bus in a PC…

I’m hoping to get these boards published somewhere but right now, I’m not clear what the licensing issues would be. These boards are not available anymore, but at some point this was a company’s IPR.

For now, I’ll keep blogging observations and see what the interest is.

Next up will be some remake of the target PCBs.

Kevin

Well that went better than expected.
Pity I don't have a Mouse Systems mouse!
It might barf due to missing INT 13 support, tho.

#VisiOn #VisiCorp #GUI #PCXT #retrocomputing

Repórter Retro 124

https://retropolis.com.br/2026/04/29/reporter-retro-124/

#ReprterRetro #68000 #68020 #ActionRetro #AdrianBlack #Agfa #AmstradCpc #Apple1 #AtariSt #BareMetal #CalebeAdventure #Codeolences #DanielFalco #DNS #DockingStation #Emuladores #ENIAC #fMSX #GutBomb #IBM #IBMPCjr #Intel #Intel8085 #KonradZuse #LGP21 #MacSE30 #Macintosh #microsoft #MSXDev #NASDAQ #OldComputersSucked #PCXT #PowerBook #RaspberryPi #RetroCollective #RetroTechChris #SanderSouza #SBC #SunMicrosystems #Tan

EDIT: It has found a home.
EDIT: I was thinking the screws weren't stock, but am told they are.
#Free to a good home: The bezel from an IBM PC XT.

#RetroComputing #VintageComputers #IBM #PCXT

I would like to find the right CGA emulator for my old XT. Has anyone used or known about chcolmon or other similar software to play CGA games on XT with Hercules?
#CGA #retrocomputing #pcxt #vintagecomputing

Yesterday I tried to play several #cga games on my old #pcxt

Since my graphics card is Hercules I usually use an emulator called 'chcolmon'. But I can't find it with that name.

Well, back to the games.

I tried to play Livingston Supongo (Opera Soft) and start fine, with their music, but with a blank screen.

However, Goody (Opera Soft), works fine. Could it be a native Hercules game?

After this I started to look for a CGA emulator, and I found hgcibm but it is too slow.

I've been sitting on a redesign of my TurboXT addon (https://github.com/hkzlab/TurboXT_Addon) for the 5160 for a few months now.

This one allows (or at least should) toggling the turbo either via external input (switch, 8255 pin), or via an I/O write.

Might decide to just send it for print at the end of the month, with a slew of other boards. Depends on my willingness to suffer at the time of ordering.
#ibm #pcxt #isa

Um computador militar nascido de uma fenda temporal

https://retropolis.com.br/2024/07/02/um-computador-militar-nascido-de-uma-fenda-temporal/

#MundoRetro #Cinema #ComputadoresMilitares #DisqueteDe514 #FitaMagntica #Impressoras #Marinha #Matricial #MoscaBranca #PCXT #ReinoUnido #TV #WTF

An early #IBM #pcxt motherboard from the junk bin at the last fair. Surprisingly, the only things I had to do to get it to start up were
- install a processor (original one missing)
- fix a ripped bodge wire
- install a new regulable ceramic cap for the oscillator (old one cracked)
- replace the two tantalums on the 12v lines (one shorted, the other would have probably followed)

Might just do the "mod" to bring it up to 1mb of RAM...

Well well well, look at what fell out of the box. Here is the missing badge of that #pcxt from the fair.

The unexpected things you find at a #fair. An #IBM5151 monitor and what seems either a #pcxt or a very well made clone.
The guy was selling random junk, and he was about to connect it to power. I stopped him and bought it as is, didn't want my car to smell like burned tantalum. 20€. Sadly, the only cheap thing I bought today, with two "untested" #megadrive consoles.the rest was more expensive.

Repórter Retro 098

https://retropolis.com.br/2023/11/30/reporter-retro-098/

#ReprterRetro #AgonConsole8 #AgonLight #Amiga #AppleII #AppleIIc #arcticretro #AS1000 #AugustoBaffa #Baffa2 #Barbie #Centurion #ColecoAdam #Commodore16 #CuriousMarc #DisqueteDe514 #DisqueteDe8 #Drygol #MquinasDeEscrever #Mitsubishi #MSX #MSX1 #MSXJa #NeXT #Olivetti #PCXT #Ringo #RMC #SayakasDigitalAttic #SegaMegaDrive #TechnologyConnections #TennisForTwo #TK83 #TRS80PC1 #UsagiElectric #ZX81

#Book8088
#Tandy1000 #PCXT

a good source of old manuals for 8bit isa cards

https://www.minuszerodegrees.net/manuals.htm

specifically including the #dtk pii-108 #rs232 card thats all over ebay. i needed the manual for the second serial port connector pinout!

Repórter Retro 093

https://retropolis.com.br/2023/06/28/reporter-retro-093/

#ReprterRetro #6800 #68000 #AdrianBlack #Aesthedes #AlsGeekLab #AnotherBoringTopic #AtariSt #AugustoBaffa #BBS #BenZotto #BITNET #Commodore64 #ComputaoGrfica #COSMAC #Doom #ethernet #FitaCassete #Hackaday #Holanda #HUG1802 #Intel #Jogos #LinguagemC #MicroCoreLabs #microsoft #ModernVintageGamer #Mouse #MSX #Multibus #NostalgiaNerd #NovaZelndia #os2 #PCXT #RCACDP1802 #recap #RetroRio #RNP #SID #SnteseDeVoz #Sphere #T

Repórter Retro 092

https://retropolis.com.br/2023/05/31/reporter-retro-092/

#RepórterRetro #adrianblack #Amiga600 #arctic.retro #BASIC #Ciência #ClubeColorRio #Commodore64C #CommodorePC20 #encontrosdeusuários #fitacassete #incêndio #MarkFixesStuff #MúsicaCountry #NoelLlopis #PCXT #réplica #RetroRio #RMC #TexasInstrumentsTI-99/4A #Ultrassom #UsagiElectric #Userlandia #VCFEast #Veritasium

It blows my mind how phenomenally good the BRIEF editor (1992) still is today. And it just performs beautifully on an XT

#pcxt #retrocomputing

A while ago I accidentally fried the EEPROM containing the BIOS in my #NuXT (IBM #PCXT compatible) machine.
I finally got around to dropping in a replacement, but also wanted to upgrade it at the same time.
At first the machine wouldn't boot and it took me a long time to realize a bug had been fixed in a later BIOS revision, requiring a wipe and reinstall of MS-DOS. A complete wipe. dd /dev/zero.
The NuXT is based on the #micro8088 but with the IDE controller at a different port, so the NuXT has its own BIOS image, however the official NuXT image hasn't been updated for quite some time, but the Micro 8088 sees regular updates.
After even more faffing about with builds and tools, I finally had an up-to-date NuXT BIOS image with both V20 and universally compatible XT-IDE option ROM, what #Monotech calls a "hybrid" BIOS.
I have put it up on GitHub, it should be slightly easier to update it in the future. And there's a binary if somebody else needs it.

Repórter Retro 090

https://retropolis.com.br/2023/03/29/reporter-retro-090/

#RepórterRetro #6502 #8-BitResurgence #ActionRetro #adrianblack #anime #Arcade #Assembler #Assembly #Austrália #bug #Commodore128 #Commodore64 #Commodore900 #consoles #COSMAC #Cromemco #DennisRitchie #fliperama #fusion-C #GEOS #HTML #IBM #internet #Japão #Kokusai #LinguagemC #mostechnology #MrLurch #MS-DOS #MSX #MSXSJC #MSXVDP #NECPC-9801 #Obituário #PCXT #PlayChoice-10 #PowerPC #programação #Protótipo #RCACDP1802

#introduction

I’m Jez from the #UK. I’ve been employed as a #SoftwareEngineer since 1994 in a variety of companies. I have also made #iOS games and contributed to #OpenSource Projects including #Groovy

I was inspired to code on the #Atari400 in the early 80’s, followed by the #BBCMicro #AmstradPCW #Amiga #PCXT and #486 PCs, I still use most of these and the #FPGA #retrocomputing remakes

I also design #MechanicalPuzzles, and enjoy the theory and technique behind #CardMagic

Cheers
Jez