Re: 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

On 12/4/2011 1:29 PM, Clay Cowgill wrote:
> I really don't think you're going to need a *lot* more performance.
> The game runs pretty smooth after the enemies get down to a certain
> point (so more CPU *after* the "back to full framerate" threshold is
> just overkill). To be 'clever', I would try something like maybe just
> a CPLD that sits on the Z80 bus and clock and watches the Z80 cycle
> and address range. Put a 16MHz crystal on the CPLD clock. Then
> (assuming this board also has all the ROMs in a fast modern memory
> like a multigame uses) I'd switch from a divided 8MHz clock to the
> 16MHz clock during an instruction fetch, or maybe just double it *any*
> time it's hitting the ROM address range.
> If a standard instruction cycle is, say, 10 T-states and the first
> four are getting the opcode, then when we see /M1 assert we could
> substitute four double-speed clock cycles. If the Z80 tolerates that
> brief over-clocking, you'd get about a 20% CPU boost for instruction
> fetches. (saves two 'slow' T-states worth of time out of the ten in
> the cycle) That would shorten the /RFSH as well, but I'd actually be
> surprised if that was used for anything in the vector games. (I'm
> thinking it's probably only used for DRAM in the frame buffer based
> games on the G80 system?)
> OTOH, I also suspect that just given how things run in the system that
> you could stick a Z80B in there and change the cpu crystal to ~10MHz
> or so and it'd probably work to speed up 'slow spots' in the game with
> essentially no effort. ;-)
> Another angle if you really just want to mess with a CPU replacement
> for fun would be to see if there were any 5V Z180's. (I think there
> were.) Like a Z80180 or Z80182... They run up to like 33MHz or
> something crazy. (That's what Namco had in that Pacman/Galaga "Class
> of 81" machine they sold for ages to run the original code without
> needing multiple Z80's and whatnot.) Might be less work without
> needing to worry about level translation and the 3.3V rail, etc.
> It might not be too much work to turn my old G80 menu system into a
> "loop counter". Basically just count how many times a loop can
> execute in between display refresh interrupts and print the number.
> That could essentially be a "benchmark" for messing with CPU speed
> tweaks then.
> -Clay
>
> ------------------------------------------------------------------------
> *From:* owner-vectorlist@vectorlist.org
> [mailto:owner-vectorlist@vectorlist.org] *On Behalf Of *Zitt
> Zitterkopf
> *Sent:* Sunday, December 04, 2011 1:26 AM
> *To:* vectorlist@vectorlist.org
> *Subject:* Re: VECTOR: Subing EZ80 microcontrollers for Z80A cpus
>
> Thanks Clay... and Bill.
> For now; I'll table this plan... Too busy with the Xy Gen and
> other projects anyway.
> I did spent about two nights thinking and planning; I think it's
> possible to do the substitution -- I'm just not sure if it'll have
> the desired impact.
> This biggest problem is the EZ80 seems to have removed the
> !refresh pin... so that would have to be duplicated somehow. I'm
> also concerned about possible uC peripherals conflicting with
> Sega's memory (or IO) map.
> As Bill mentioned; the PCB would have to have a 3.3V regulator...
> and the EZ80 doesn't come in a package I really like. BGA or
> 144pin LQFP... both may be on the big side for a DIP sized drop in.
> I wouldn't really care about "loosing" 90% of the EZ80's
> functionality; as long as it "improved" the lag problem.
> I know Z80s are widely available as pulls / etc; I just wanted to
> get a pipelined version to see what it did to the lag.
> A side effect; might be that highscores could be saved in flash;
> but still a complex project I'm not motivated to tackle yet.
> Too bad I have a day job. ;P
> John
>

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Received on Sun Dec 4 16:26:47 2011