https://yeokhengmeng.com/2023/09/hdmi-i ... ntage-pcs/

I reckon a 6502 could bank switch to talk to an ISA bus without too much difficulty, right?

Neil

I'm sure there have been some ISA bus based 6502 or 65816 systems... I think the '816 might be a better option too, but we're back to the issue of RAM vs. CPU processing time... When you have 64KB of RAM for Video and you want to clear it in software by pixel-poking, then it takes time. Draw a line? Even more time - and 3 times more if it's less than 8 bits per pixel (read/modify/write, but twice the RAM for 8 BPP - you can't win!)

It's no surprise that in the early 80's hardware assist started to appear along with many different, novel and weird arrangements for pixel planes, sprites, tiles, blitters and who knows what else...

Remove the pixel poking and it opens up more possibilities - just as the serial graphical terminals did in the 70's - Tektronix 4014 and so on, and modern GPUs do today.

My Ruby system effectively has an HDMI output, but it does that via a serial line to my Linux Desktop which runs a smart terminal program that interprets high level commands over the serial line. One day I'll replace this with a parallel interface to a small $5 SBC system with an HDMI output - but then I'll need a separate monitor, so still can't win

Cheers,

-Gordon

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Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/

Still interesting to play with though I'm sure! Hopefully the register interface is well-enough documented. For PC use it's going to include a video BIOS "ROM" to abstract the hardware details, but obviously that's not going to run natively on a 6502!

I found a Roland LAPC-I in a box from my old garage about a year ago, and have some vague plans to hook that up to a 6502 one day, and send commands to it through the ISA bus. It only requires a very limited subset of the bus though, compared to a video card, otherwise I don't think I'd attempt it.

I think the most interesting/useful part of that board is the DVI interface chip, which is apparently a standard part that anyone could buy and use (if they have the skills to solder it in) and thereby connect a parallel pixel value output to a standard DVI-D or HDMI monitor.

All the stuff on the FPGA is specific to the ancient PC standards being emulated, including the ISA bus and of course the 6845 CRTC (which is relatively well documented in itself), plus some workarounds to better fit modern display hardware (which often doesn't go down far enough to match a PAL or NTSC standard frame timing). By the sound of it, the register set will be a standard MDA/CGA set, but with exploitation of some of the more obscure quirks being complicated by the differences in output timing and small inaccuracies in the emulation. However, MDA/CGA is a very limited capability to aim for, and I think a lot of homebrewers would prefer more flexibility.

Yeah, CGA and similar ancient PC standards aren't my cup of tea either. But of course that DVI interface chip is capable of far more. Datasheet attached.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html