John Bennett
Senior Member
[ukvac] Tech: Pacman multigame problem
I thought it was worth reporting this as it might save someone
some trouble...
I have a Pacman bootleg cocktail board (marked OVG-11) that had
been hacked to run Ms Pacman. I decided to convert it to run both
Pacman and Ms Pacman (switchable) by following the guide on:
http://marvin3m.com/video/pacman.htm
After completing the conversion I found that Ms Pacman worked but
ordinary Pacman didn't. I checked my conversion work several times
and it was correct. After some probing I came to the conclusion that
Pacman was crashing on start up. After much head-scratching I ended
up digging into the code for the games and found something important:
Midway Ms Pacman runs in Z80 interrupt mode 1 and Midway Pacman runs
in Z80 intrerrupt mode 2. Mode 2 requires a little bit of extra
hardware (a latch to store part of the interrupt vector). I
checked my bootleg board and found that this hardware was missing
(the Z80 IORQ pin was not connected to anything).
After more digging I found that Namco Pacman runs in Z80 interrupt
mode 1! I burned a new EPROM containing Midway MS Pacman and
Namco Pacman and now I have a working multigame.
To summarise things: Midway Pacman will not work on some bootleg
Pacman boards (unless the code is hacked). If you find this,
try the Namco Pacman ROMs.
Gary.
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
DATA Imported from archives: originally posted by shepg2002 (lists@ntlworld.com)
I thought it was worth reporting this as it might save someone
some trouble...
I have a Pacman bootleg cocktail board (marked OVG-11) that had
been hacked to run Ms Pacman. I decided to convert it to run both
Pacman and Ms Pacman (switchable) by following the guide on:
http://marvin3m.com/video/pacman.htm
After completing the conversion I found that Ms Pacman worked but
ordinary Pacman didn't. I checked my conversion work several times
and it was correct. After some probing I came to the conclusion that
Pacman was crashing on start up. After much head-scratching I ended
up digging into the code for the games and found something important:
Midway Ms Pacman runs in Z80 interrupt mode 1 and Midway Pacman runs
in Z80 intrerrupt mode 2. Mode 2 requires a little bit of extra
hardware (a latch to store part of the interrupt vector). I
checked my bootleg board and found that this hardware was missing
(the Z80 IORQ pin was not connected to anything).
After more digging I found that Namco Pacman runs in Z80 interrupt
mode 1! I burned a new EPROM containing Midway MS Pacman and
Namco Pacman and now I have a working multigame.
To summarise things: Midway Pacman will not work on some bootleg
Pacman boards (unless the code is hacked). If you find this,
try the Namco Pacman ROMs.
Gary.
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
DATA Imported from archives: originally posted by shepg2002 (lists@ntlworld.com)