Re: C128 Z80?

David Murray wrote:
an emulator to run cartridge ROM images from other Z80-based video game
systems like the Nintendo GameBoy or Sega Master System? I doesn't seem
like it would be too difficult?

It doesn't seem trivial either.. Just for an FYI, here are the specs
on the gameboy:

CPU: Z80 at 4 Mhz
RAM: 8K
Screen: 160x144 with 4 shades of gray.

The ROM cartridges range from 32 KB to 256 KB. So only the smaller
carts would even be feasable.

The main two issues I see is that the Z80 in the C128 can't run (so
I'm told) at a true 4 Mhz..

In the C128 the Z80 runs at 4 MHz half of the so, i.e. effectively it runs at 2 MHz.

Then you have the issue of the screen.
The resolution isn't a problem but having 4 shades of gray might be..

The VIC can produce 5 shades of gray (counting black and white as a shade of gray). The multicolor mode is adequate.

The VDC can produce 4 shades of gray but can only produce two colors in a 8x1 pixel block.

I think with the multicolor mode you might be able to achieve this but
the aspect ratio will be all wrong. the music would be optional, but
could probably be emulated. I think the main issue is that there just
isn't enough horsepower.

Agreed. Even if the Z80 ran at 4 MHz it would still be insufficient. The processor would still have to convert screen memory every time the screen contents change since the video memory layout of the gameboy is no doubt different than the VIC.
.

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