Jo22 wrote on 2021-03-10, 07:23:

Interesting idea, since both CGA and HGC (aka MGA) are using the same CRTC and can co-exist, even. They are like brothers, so to […]
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Benedikt wrote on 2021-03-09, 22:22:

A CGA card with HGC+-style RAM font support would also be interesting. Or a HGC+ clone in general.

Interesting idea, since both CGA and HGC (aka MGA) are using the same CRTC and can co-exist, even.
They are like brothers, so to say. That's why I added a HGC clone in my XT class PC in first place, also.

The HGC clone card can be used as as a primary device (MODE MONO) or as a secondary device (MODE CO80).
HGC's graphics mode can also be used in Half-Mode (MSHERC.COM /HALF) without interferring with CGA's video memory.

Another interesting idea would be to implement Hercules InColor some day.
There's not much software support (MS Flight Sim, CompuShow2000 etc), but the hi-res graphics are maybe nicer than EGA. ^^

If I can get my hands on any/all of these, I would be happy to reverse engineer them. I have the time, just not the money 🤣. Gotta love being a college student.

There is an interesting related thread on the VCFED forum for those that are interested.

Hi,

You can check this 😀
https://www.andavno.com/?p=478

I found him when looking for a POST Card.

As when we buy a POSt Catd (The PIC/ISA) one on ebay, they don't work, the ISA bus is reversed.

FreddyV wrote on 2021-03-12, 13:55:

You can check this 😀
https://www.andavno.com/?p=478

Yeah. We've been talking about his card.
Incidentally, he also posted to the thread that is linked above a couple of days ago.
According to his own words, he still plans to publish his design files at some point.

maxtherabbit wrote on 2021-03-09, 15:19:

yes I agree, Tandy would make this endeavor worthwhile

Agreed. That would indeed make it a lot more interesting, especially combined with the Tandy 3-voice ISA cards that have already been developed.

Wouldn't it pose a much bigger challenge w.r.t. (shared) memory mapping, though? How could one map the memory on such an ISA graphics card to the lower 128KB of RAM address space on the host system? And I mean in a way that would not require a 386 or higher.

digger wrote on 2021-03-12, 23:52:

How could one map the memory on such an ISA graphics card to the lower 128KB of RAM address space on the host system? And I mean in a way that would not require a 386 or higher.

My former Tandy 1000rl had 768k of which 640k was usuable

The 128k just sat in the beginning of the upper memory area

Jager wrote on 2021-03-09, 21:30:

https://www.andavno.com/?cat=8 - chip-for-chip replica.

Nice project, however it seems there aren't any updates in the last year?

rmay635703 wrote on 2021-03-13, 02:09:

digger wrote on 2021-03-12, 23:52:

How could one map the memory on such an ISA graphics card to the lower 128KB of RAM address space on the host system? And I mean in a way that would not require a 386 or higher.

My former Tandy 1000rl had 768k of which 640k was usuable

The 128k just sat in the beginning of the upper memory area

Maybe I should have clarified my question a bit more. From what I have understood of how the shared video memory in the Tandy 1000 (and the PCjr?) worked, is that it encompassed the first (lowest) 128KB of the conventional memory. And since (I assume) any existing on-board memory in most PC/XT systems counts up from the bottom, how would it be possible to have the video memory of such a hypothetical Tandy 1000 compatible ISA graphics card mapped to those first 128KBs of conventional RAM? I guess it would be practical if all on-board RAM chips were removed from the motherboard and to then have such a card provide all of the conventional RAM, with the first 128KB being shared between the card's video logic and the CPU. But on an any system with a data bus to the on-board RAM that is wider than 8 bits and/or faster than the ISA clock speed, that would result in a downgrade in terms of memory performance. So can anybody think of a performant solution for 8086 and 286 systems that have a faster memory bus than 8-bit ISA, yet don't yet support memory shadowing, like 386 and later CPUs do?

I guess perhaps a 16-bit ISA card in the case of 286 systems?

digger wrote on 2021-03-13, 14:59:

Maybe I should have clarified my question a bit more. From what I have understood of how the shared video memory in the Tandy 1000 (and the PCjr?) worked, is that it encompassed the first (lowest) 128KB of the conventional memory. And since (I assume) any existing on-board memory in most PC/XT systems counts up from the bottom, how would it be possible to have the video memory of such a hypothetical Tandy 1000 compatible ISA graphics card mapped to those first 128KBs of conventional RAM?

I believe I have read somewhere that only the PCJr. did it that way and that the Tandy machines actually put the shared (or exclusive) video RAM on top.
Since virtually all software for the 16-color modes is written for Tandy machines, anyway, we could therefore get away with putting 128KiB on a graphics card.