I'd recommend looking over at the retrobrewcomputers.org forum and wiki - there are loads of wacky designs on there, including ISA and ECB backplanes.

The biggest issues with using things like VGA cards on old microprocessors like the 6809 is that most are going to struggle to fit even one page of VGA memory in their address space.

It's possible, but I don't think it would make any sense.

6809 = 8 data bits, 16 address bits, memory-mapped I/O only.
ISA (in it's simplest variant!) = 8 data bits, 20 address bits, both memory-mapped and separate I/O space.

So, you would need somewhat complicated logic to glue them together...

Grzyb wrote on Yesterday, 07:05:

It's possible, but I don't think it would make any sense. […]
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It's possible, but I don't think it would make any sense.

6809 = 8 data bits, 16 address bits, memory-mapped I/O only.
ISA (in it's simplest variant!) = 8 data bits, 20 address bits, both memory-mapped and separate I/O space.

So, you would need somewhat complicated logic to glue them together...

Thanks. So I'd probably be better off pursuing a custom bus and custom i/o cards (gfx/audio/net) tailored more to the 6809.
Maybe I'll look into using the Vera video/audio board from the Commander X16 project...

I've actually thought about doing this!

I use the 6809 a LOT (most powerful 8-bitter I've seen), nowadays mostly in various control applications where I "talk" directly to then with a serial TTY interfaces.

I have made a 6845 based monochrome video display (with a parallel keyboard) 24x80 text - I wouldn't try to do anything graphic unless you implement some sort of paged memory "window", and I'd guess "VGA" is going to be more complex than you'd want.

I've also done some NEC 765 base floppy interfaces, if you can find an old PC floppy controller this could work as well.

Have a look at my D6809 (portable system built in 1980s): http://dunfield.classiccmp.org/d6809/index.htm
If you have a DOS system (or DosBox), you can even experience actually running/using it as I created a pretty accurate emulator for it "back in the day" - this is actually what I still use to test much of my 09 code.

As you are going to writing your own drivers, I don't think endian matters much.

Obviously any on-board ROM is going to be useless!

You may run into issues with 16 bit IO, maybe needing mostly original PC(8088) IO Cards, which can be tough to find these days.

What I've thought about building a rudimentary ISA interface for is mainly to easily talk on an NE2000 network interface. I'd like to implement a DDLINK LAN server one of my larger 09 systems just to make it "easy" to put stuff on/off - I've done this on an few ARM based system, talking to a NE2000 isn't hard.

Grzyb wrote on Yesterday, 07:05:

6809 = 8 data bits, 16 address bits, memory-mapped I/O only.
ISA (in it's simplest variant!) = 8 data bits, 20 address bits, both memory-mapped and separate I/O space.

Probably not as tricky for most IO cards ... what I've done in most of my 09 systems is to reserve a block of address space starting at 0000 which is "IO", and it's not hard to make a select for that range appear on an interface as a separate IO bit. Many of the most useable cards are going to be I/O only, with on board ROM being useless/redundant.

Addressable memory (like a video display) is going to be implemented as a smallish (maybe 4-8k) "window" in the 6809 address space, with IO "ports" to make higher addresses available if needed.

Using an ISA VGA card on an AVR

Z80 isa VGA https://ciernioo.wordpress.com/2016/03/21/80- … a-new-solution/

https://hackaday.com/2024/11/30/arduino-vga-t … -fashioned-way/
https://github.com/marcin-chwedczuk/mega-iso-vga

avr using ISA ethernet card https://dclausen.net/projects/avr_ethernet/dc … 281_writeup.pdf
pic using ISA NE2000 ethernet https://picnic.sourceforge.net

there used to be http://tinyvga.com/avr-isa-vga but its gone 🙁
"This project connects ISA VGA card to Atmel AVR ATmega 128.
Supported cards
The following cards are supported:
Realtek RTG3105iEH
Trident TVGA9000i
Trident TVGA9000B
Trident TVGA8900CL
Cirrus GD5401
Cirrus GD5402
Oak OTI077"

should be available thru webarchive https://web.archive.org/web/*/http://tinyvga.com/files/* but cant confirm, its currently struggling to open and downdetector shows its global, , files are tiny so attaching

TLDR yes its possible and the easiest way to get decent video output. You will have to take care of card initialization tho, either capturing what original BIOS is doing or executing VGA BIOS in interpreter on your platform, or copying init routines from one of the projects above

PS: its one of those things I have always been fascinated about, I even just found my post from 2002 to comp.arch.embedded about this subject :]