RE: Subing EZ80 microcontrollers for Z80A cpus

Get a Z80H, and skip the last divider U28 on the XY timing board - should
push the EXT CLK to 7.5MHz.

Thanks,

Chris Brooks

From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Clay Cowgill
Sent: Sunday, December 04, 2011 5:50 PM
To: vectorlist@vectorlist.org
Subject: RE: VECTOR: Subing EZ80 microcontrollers for Z80A cpus

Ahhh, interesting. Makes it easy to intercept at least.

The big question then is really if the game is running async from the frame
rate or not. It's just been too long since I was mucking about and patching
those to remember anymore. I suppose a debug build of MAME would probably
be educational if it has a t-state count in the debugger. Set a break point
on the external interupt service routine and see if you get about the same
number of t-states every frame.

I'm basing this off of a vague recollection though too-- what I recall is
that when my multigame menu graphics got too complex it simply didn't draw
some of them (suggesting it had a fixed amount of time to finish vs. a
variable framerate that slowed down and flickered like an Atari AVG would).
I had converted a bunch of Borland BGI stroked fonts to the G80 vector
format and immediately ran in to problems with draw time. (In particular I
remember only getting one of my "selection arrows" on the screen.)

I suppose that still makes for an easy test-- just keep the external clock
select high and clock the Z80 separately and see if the game runs OK or not.
;-)

-Clay

  _____

From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Vector Labs
Sent: Sunday, December 04, 2011 1:23 PM
To: vectorlist@vectorlist.org
Subject: Re: VECTOR: Subing EZ80 microcontrollers for Z80A cpus

Actually the clock for the Z80 is generated on the XY Timing board, not the
CPU board.
If you look at the Z80 pin 6 you would assume that the on board 8Mhz crystal
/2 = 4Mhz
but in reality it uses the XY timing board crystal which is 15.46848Mhz /4
= 3.86712Mhz.
At least it is on all the board sets that I have.

Mike

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Received on Sun Dec 4 19:17:29 2011