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Design my own computer based on the Zilog Z80


This topic contains 3 replies, has 4 voices, and was last updated by  tomsmith 2 years ago.

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Design my own computer based on the Zilog Z80

21/03/2018 at 11:28

I’m designing my own computer based on the Zilog Z80. It has 256KiB of static RAM with paging as well as a few megabytes of flash memory. Everything is going along pretty well until * BAM * I hit a dead end.

The problem that I am having is designing a video controller. I was thinking about some kind of a terminal or display. A 24×80 or 25×80 terminal would be wonderful. However, even a 640×480 VGA display would take up enormous amounts of memory.

640 * 480 = 307.2 Kbits

That is even more than the amount of memory addressable by the Z80 at one time!

Also, if I want color, say, one bit per color, I would need 3 bits per pixel.

307.2 Kbits * 3 = 921.6 Kbits

In addition, wouldn’t it need to be dual-ported to allow access from Z80 and the monitor?

Because this is extremely difficult to implement in software and hardware, would it be a good decision to use a character ROM such as GSC320 from kynix: http://www.kynix.com/? It would be very difficult for me to get fuse-link PROMs or UV EEPROMS. What should I do? Can I put a character ROM in flash memory? How would I implement it in the controller? How do I tell the character ROM which character to spit out? Should I even use VGA? Would component video (NTSC or PAL) be easier than VGA?

If a good system can be designed, perhaps we can even use it for microcontrollers! Give me all you got, I need as many ideas as possible.

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11/08/2018 at 20:58

i would make sure its windows 10 compatible first.

11/08/2018 at 21:45

If it is going to be used as a microcontroller, then it doesn’t really need a display any more complex than a  Sinclair Spectrum or even a Sinclair ZX81.

19/06/2019 at 11:13

You can refer to here


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