Z280 to Z80 adapter revisit

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By lintweaker

Master (151)

lintweaker's picture

16-11-2018, 13:34

Back in 1995 I did some experiments with a Z280 in a Sony HBF900. I did not get past displaying some text in screen 0 width 80.
Now I am playing again with a Z280, this time in combination with my DIY MSX. I have build a new Z280 module as I cannot find my original Z280 to Z80 DIP40 adapter :-(.

I can boot to MSX1 with the Z280 without issue. MSX2 will not boot, even after disabling the Z280 internal cache and adding IO and memory wait states.

Does anyone have a Z280 to Z80 adapter schematic laying around? I cannot find the one I used in 1995, maybe I am missing something.

Note: one of the issues with Z280 is the /M1 signal not being fully Z80 compatible. This causes issues with the MSX /M1 wait.

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By Edevaldo

Expert (126)

Edevaldo's picture

17-11-2018, 01:54

Well, I do not know the answer to your question but I got curious...

How much faster to you expect the Z280 to be? At which frequency to you plan to run it?

It may not be too hard to fix the M1 behavior with some external logic. If you give some detail maybe I could help with that.

By lintweaker

Master (151)

lintweaker's picture

17-11-2018, 09:07

Edevaldo wrote:

Well, I do not know the answer to your question but I got curious...

How much faster to you expect the Z280 to be? At which frequency to you plan to run it?

That is what I am trying to find out Smile Currently the CPU runs at 7.16MHz with the bus speed a normal 3.58MHz MSX speed. The plan is to get the CPU running at 14.32MHz while the bus remains at 3.58Mhz. This needs some trickery with the /WAIT line at bootup. I have this in place but it is not working right now. You cannot change the speed after booting (like with the Z180).
The CPU does have cache but that has bugs in Z80 BUS mode so has to be disabled, it does not like self modifying code. There are lots of new instructions which could help performance, but that is another story. R800 code should run.

Edevaldo wrote:

It may not be too hard to fix the M1 behavior with some external logic. If you give some detail maybe I could help with that.

What information do you need?

By erpirao

Paladin (912)

erpirao's picture

17-11-2018, 20:39

By erpirao

Paladin (912)

erpirao's picture

17-11-2018, 22:02

I'm sorry that link was from another user, anyway we expect news

By lintweaker

Master (151)

lintweaker's picture

18-11-2018, 08:25

erpirao wrote:

this?

Thanks. Reading through it seems mainly about using a Z180, with a few mentions of Z280.
I really hope somebody has the old schematic for a Z280>Z80 adapter.

By erpirao

Paladin (912)

erpirao's picture

19-11-2018, 15:32

I think I'm going to buy a msx2 just for that experiment (I've already bought 5 z8028010) ...

By msd

Paragon (1372)

msd's picture

19-11-2018, 20:06

Did anybody ever try to find r800 chips?

By zett

Hero (548)

zett's picture

19-11-2018, 20:09

buy a victor hc-95a it got a z180 and z80

By erpirao

Paladin (912)

erpirao's picture

23-11-2018, 16:15

the z280 is a derivative of the Z800 from which the R800 evolved, so the closest thing to the R800 that there is is a z280.
look for a real R800 .. it can be very difficult (rather impossible)

By zett

Hero (548)

zett's picture

23-11-2018, 16:28

why not work on a fpga r800. would be nice for the future of fpga msxing. its always more future proof.

And r800 is proven to be work see turbo R.
so why reinventing ?

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