Accidentally I came across a very unusual computer which uses the 6502 as a graphic co-pro!
http://www.vcfed.org/forum/showthread.p ... r-Yes-CP-M
A man is seeking some help...

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my blog about processors

A OEM version of the Ontel Amigo.

https://www.old-computers.com/museum/co ... t=1&c=1151

Related to CW/P's Cortex.

https://www.old-computers.com/museum/computer.asp?c=899

It quite interesting to see a Z80 paired with a 6502. The Z80 is a clear choice for a CP/M machine, so the 6502 must have been a specific choice for good reasons to be the graphics processor. The display is 640x300 and (according to the Argentine advert) offers 8 shades of monochrome. The 6502 in this system has as much as 40k or maybe even 44k of RAM, which seems like a lot but only barely enough for a 2 bit deep display at that resolution. So maybe the 8 shades means something else or maybe there were multiple resolutions available.

It could reasonably be a bitplane design, with a 24KB framebuffer mapped three times and a 20KB workspace. But I can't seem to find where the memory is triplicated, as it would need to be.

In the PCB photos, there's a big bank of twenty Am9016 DRAM chips in the bottom left corner, with blank pads for two more. That's a 16Kx1 part, for a total of 320Kbit, 40KB, but there would be some 16KB area with only half the data lanes populated. The extra pair of chips would bring it up to 44KB, if fitted. So this is clearly the 6502's memory.

In the top-left corner there's a bank of eight MB8264s - that's a 64Kx1 part. That must be for the Z80.

Ah, I wonder if that's 32k of byte wide memory and 16k of nibble wide? Nibble wide memory might be for intensity or similar, either as pixels or as lower-resolution attributes. The extra two chips would bring that extra area up from 4 bits wide to 6 bits wide.

Yes, I suppose attribute mode is a possibility. For every group of 8 pixels there would be a full byte indicating which are foreground and background, and either 4 or 6 bits indicating the intensity of each (4 or 8 levels, twice). You can do some reasonable graphics with that, even if the attributes cover pairs of scanlines.

There would need to be 24KB mapped to pixels and 12KB mapped to attributes at any one time. Maybe there is a hardware scrolling system that makes use of more than that. The 6845 at bottom right should be capable of that, certainly. But some RAM would also need to be reserved for ZP and stack usage by the 6502, so it's not a completely free allocation.