RE: Revisited: Sega XY freeplay

It's all software. You can find it pretty close to the beginning of the
code in Star Trek at least.

Star Trek code is a real bastard to follow. They make extensive use of the
software reset in the Z-80 for jumps, and then do indirect jumps through RAM
to make a little event dispatcher out of it.

With a debugger build of MAME now though it should be easy to spot. Worst
case, just disassemble the whole game and grep out the port that the coin
switches are connected to. Then just look at the source around the areas
where the port are access and see which one is testing for the coin
switches. (Alternatively you could use breakpoints in MAME set to the
addresses where the port accesses are and just run the game and hit 1 or 2
and see if the breakpoint triggers...)

Once you locate the coin switch reads, just step through the code and fine
the timing loop. From there, hack on the ROM image (I wish MAME's debugger
would let you modify program memory...) and test to make sure you killed the
timer. ;-)

Since I never seem to get around to this, I'll look for my disassemblies of
all the G-80 stuff. I think I noted the coin-timer in at least one...
Probably a two-byte patch to just jump over it...

-Clay

> ----------
> From: Mark Jenison[SMTP:jenison@cig.mot.com]
> Reply To: vectorlist@lists.cc.utexas.edu
> Sent: Wednesday, September 01, 1999 9:20 AM
> To: vectorlist@lists.cc.utexas.edu
> Subject: Revisited: Sega XY freeplay
>
> I had to resubscribe to vectorlist today...apparently I was unsubscribed
> (and
> just after my post about the way reply was set up...how coincidental!). I
> thought the list was awfully quiet. :-)
>
> Does anyone understand how Sega implemented the timed-coining for their
> vector
> games? Is it all in software, or is it hardware?
>
> ----------------------------------------------------------------------
> Mark Jenison E-mail address: jenison@cig.mot.com
> Cellular Infrastructure Group Motorola--Arlington Heights, IL
> ----------------------------------------------------------------------
>
Received on Wed Sep 1 13:11:12 1999