Hello, thanks for the answer.
Nice to know you were the system engineer on all video hardware at AT&T. I have accumulated lots of questions on this matter.
From when I was a 20yo man (now I'm a 58yo OLD man) I was wondering how to extend the WD/Paradise video modes onto the Olivetti M240 (or AT&T PC6300 WGS) Olivetti made VGA card. That card used the PVGA1A same as the VDC600, could work in a 8 or 16 bit bus and had only 256KB of memory. So only the 640 x 400 x 256 video mode was available but not supported by the BIOS developed by Olivetti.
The VDC600 practically manages the Olivetti native video mode 0x40 and 0x48 (640 x 400 in 16x8 and 8x8 font size) passing the control to the standard BIOS. So that resolution non managed within the EPROM installed on the VDC600.
My question was if the VDC600 was also handling the other 256 video modes that PVGA1A could handle, such as 640 x 400 x 256 colors and 640 x 480 x 256 colors (if the 512KB of memory was installed).
I'm currently reverse engineering the BIOS of the VDC600.
I also have in my collection some VDC400 (a copy of the original M24/PC6300 video board made by STB System based on the gate array STB developed). There was also a BIOS onboard so the card could work also on a computer not from AT&T.
I also have the VDC750. One curiosity I have is if the video BIOS of the VDC750 supports also the 640 x 400 x 16/64 colors additional video mode similar to the EGA compatible 640 x 350.
Another fun thing of the VDC750 is that is uses the standard DB25 connector similar to the one equipping the Olivetti original monitor and can work at 640 x 350 with only 16 colors, this with a smaller footprint on the screen. I have the installation manual of the VDC750.
Another question: do you know why AT&T decided to source from another manufacturer (not from Olivetti) the CRT314 and CRT319, which were CGA/OLIVETTI/EGA compliant monitors but working only at 110 Volts 60 Hertz?
Ok, I will try to find the original floppy. But I'm sure the image is available on the net. Was the manual in TXT format? Very difficult to have pictures in a TXT file format.
Did you ever travel to Ivrea or to the Paradise headquarter?
Do you have, by change, the technical reference of the Paradise Chips PEGA2A and PBI?
Or the BIOS listings of any of the VDC400, VDC750 or VDC600 boards?
Lots of questions in BOLD for your convenience.
Thank you in advance for your eventual answers.
Regards, Vincenzo (from Italy)
PS: attached the analysis made by the AI Claude on the VDC600 BIOS vs the Olivetti M24 video modes 0x40 and 0x48.
I'll try to respond to your questions, although it was almost 40 years ago...
I don't recall if the VDC600 handled the other 256 color modes. I think in those days we were OEM'ing display cards from STB ("Simply The Best"), a third-party vendor located in Texas; although we were also working with Western Digital (who owned Paradise at the time): I definitely remember working with WD on the VDC800/VDC850 8514/A cards. IIRC, the VDC600 was a pretty standard off-the-shelf VGA card without too much customization. I think it was our first card that wasn't backward compatible with the older 25-pin monitors: VGA used an RGBA analog signal, but the older monitors used an incompatible RGBI digital signal; not to mention that the old monitors only went to 400 lines and VGA went up to 480 lines (I think we might have gone to 800x600 and 1024x768, but it's too long ago to remember). After leaving AT&T Computer Systems I worked for AT&T Microelectronics in Allentown designing our own VGA chips and boards, so everything in my memory kindof mushes together.
I think the VDC750 did support some 640x400 modes. That was the last card we shipped with the 25-pin connector to work with the older monitors, and it was a pretty big sales point to our customers that while IBM was forcing everyone to buy a new monitor for EGA, we were still supporting the same monitors we had originally shipped with the old PC6300.
As for monitors, I don't recall what happened with the CRT314/CRT319 or if/when we switched away from Olivetti. I worked on the CRT365 and CRT395, which were large/high-res workstation monitors we sourced from Capetronic in Taiwan for use with the VDC800. Those were beautiful monitors.
Sorry, I don't have any other info- that was all from the beginning of my career, and I'm just getting ready to retire now.
I never travelled to Italy to visit Olivetti, I joined as the Olivetti relationship was starting to trail off. The org I joined had already shipped the PC6300+ and we were designing our own 386 PC. I did hear stories from people who had travelled to Italy, although the only one that sticks in my head was that the Olivetti cafeteria served wine.
I spent quite a bit of time at Western Digital in California working with them on the 8514/A product.
I will leave you with a two stories:
1. The 8088 processor used an 8-bit bus and automatically decomposed 16-bit IO write operations into two 8-bit writes: first to the lower address, then to the upper address.
The CGA register set used an 8-bit index/data register design where you write the index register first and then write the data value to the next address:
| Port | Function |
|---|
| 3D4h | CRTC index register |
| 3D5h | CRTC data register |
Lots of application programmers realized that one could perform a single 16-bit write to the index register and the chip would automatically decompose this into an index register write of the low 8 bits followed by a data register write of the upper 8 bits.
But the PC6300 used a fully 16-bit 8086 processor, so this decomposition took place outside the processor in custom Olivetti hardware. And they got the order backward, so a 16-bit write resulted in the top 8 bits being written to the data register followed by the lower 8 bits being written to the index register. Lots of software was broken due to that issue.
2. On my first day at work in the summer of 1986, my boss handed me a PC6300 display card and said "figure out how this works; we need to build our own version". Recall this was the weird PC6300 form factor where the card itself was the bus edge connector.
Anyway, I went to my new office and spent the next two weeks buzzing out the card to figure out how it worked. At the end of that time I met with my boss and said "I think I understand, but it would have been much easier if we had schematics". At which point he said "Oh, I forgot to give you those?", and he turned around and fished out the schematics from a pile on his desk.
