[ukvac] TECH: Namco/Atari Dig-Dug
Hi All,
Non-techy people leave now. Go and clean off your viruses.
Me and Mike Mnemonic were fixing some Atari Dig-Dug PCBs last night, and it
was a bit of a test!
Atari licenced Dig-Dug from Namco. All of the released Atari circuit
diagrams we have, have IC references which appear to be references from the
Namco PCBs, not the Atari ones - or at least not the Atari ones that we
have. This makes it extremely difficult to workout what is where.
The PCBs we had have three Z80 processors in a line at one end of the PCB -
looking quite similar to a Centipede or Asteroids PCB in size and layout. In
some Atari in-house circuit diagrams of Dig-Dug, kindly lent to us by
XY-Man, there is a picture of a Dig-Dug which looked more like a Pole
Position PCB than our Dig-Dug ones, judging by the postions of the 3 Z80s,
which are dotted around the PCB.
Furthermore, the circuit schematics seem lacking in detail when compared
with those of, say, Centipede, Missile Command or Asteroids. In fact you
could say they were crap, as Atari moved from 2 big 2-sided sheets to loads
of small sheets, just like Star Wars (Grrr). There's no descriptions of how
the circuits work or any of the other nuggets that are all over other early
Atari PCBs schematics. Most annoying is that there's no Signature Analysis
info on them. I'm guess this is what happens when a game is licenced. Even
the notes from the Atari technicians in Ireland (thanks XY) are a bit
sparse - as if they didn't really have a complete handle on how they worked,
either.
This is all made worse by the fact that there are 3 Z80s. We worked out that
these are prioritised: 1st does main processing, 2nd does the sprites and
the 3rd does the sound. This is quite different (more advanced?) from most
Atari PCBs of the same era. What looks really odd (clever?) is that the 3
CPUs share the same address and data bus, each processor being able to give
priority to the next. I cannot so far work the reason for doing this - it
looks like a big hardware overhead for no advantage, as only 1 Z80 can use
the address bus at a time. Each of the Z80s has it's own ROMs to run it, but
no RAM, so they can't 'play on their own'.
So the questions are these:
How many different PCB styles of Dig-Dug are there, Atari and Namco? Which
ones made it to the UK?
Are there any circuit schematics that reference the ICs in the postions on
the PCBs that we have?
What other documentation is available to describe how these circuit diagrams
work?
What Namco games would have a similar PCB circuit design and is there any
descriptive text that would describe them?
How do the 3 Z80s co-reside on the same address and data buses (this one's
really confuzing me!)?
Any pointers gratefully accepted.
As it happens, both the PCBs are now working perfectly (yours too Rav!). We
fixed them by a bit of intelligent guess work, and Lady Luck shone on us.
BUT you know how it is - we've hit something we don't understand and that's
far more interesting than playing Dig-Dug ever was...
Cheers,
D-Type (Phillip Eaton)
Home: +44 (0) 1536 268424
Work: +44 (0) 1536 760156
Mobile: +44 (0) 7775 726366
Fax: +44 (0) 870 055 4815
Email: phil@pjeaton.demon.co.uk
Website: http://www.pjeaton.demon.co.uk
Hi All,
Non-techy people leave now. Go and clean off your viruses.
Me and Mike Mnemonic were fixing some Atari Dig-Dug PCBs last night, and it
was a bit of a test!
Atari licenced Dig-Dug from Namco. All of the released Atari circuit
diagrams we have, have IC references which appear to be references from the
Namco PCBs, not the Atari ones - or at least not the Atari ones that we
have. This makes it extremely difficult to workout what is where.
The PCBs we had have three Z80 processors in a line at one end of the PCB -
looking quite similar to a Centipede or Asteroids PCB in size and layout. In
some Atari in-house circuit diagrams of Dig-Dug, kindly lent to us by
XY-Man, there is a picture of a Dig-Dug which looked more like a Pole
Position PCB than our Dig-Dug ones, judging by the postions of the 3 Z80s,
which are dotted around the PCB.
Furthermore, the circuit schematics seem lacking in detail when compared
with those of, say, Centipede, Missile Command or Asteroids. In fact you
could say they were crap, as Atari moved from 2 big 2-sided sheets to loads
of small sheets, just like Star Wars (Grrr). There's no descriptions of how
the circuits work or any of the other nuggets that are all over other early
Atari PCBs schematics. Most annoying is that there's no Signature Analysis
info on them. I'm guess this is what happens when a game is licenced. Even
the notes from the Atari technicians in Ireland (thanks XY) are a bit
sparse - as if they didn't really have a complete handle on how they worked,
either.
This is all made worse by the fact that there are 3 Z80s. We worked out that
these are prioritised: 1st does main processing, 2nd does the sprites and
the 3rd does the sound. This is quite different (more advanced?) from most
Atari PCBs of the same era. What looks really odd (clever?) is that the 3
CPUs share the same address and data bus, each processor being able to give
priority to the next. I cannot so far work the reason for doing this - it
looks like a big hardware overhead for no advantage, as only 1 Z80 can use
the address bus at a time. Each of the Z80s has it's own ROMs to run it, but
no RAM, so they can't 'play on their own'.
So the questions are these:
How many different PCB styles of Dig-Dug are there, Atari and Namco? Which
ones made it to the UK?
Are there any circuit schematics that reference the ICs in the postions on
the PCBs that we have?
What other documentation is available to describe how these circuit diagrams
work?
What Namco games would have a similar PCB circuit design and is there any
descriptive text that would describe them?
How do the 3 Z80s co-reside on the same address and data buses (this one's
really confuzing me!)?
Any pointers gratefully accepted.
As it happens, both the PCBs are now working perfectly (yours too Rav!). We
fixed them by a bit of intelligent guess work, and Lady Luck shone on us.
BUT you know how it is - we've hit something we don't understand and that's
far more interesting than playing Dig-Dug ever was...
Cheers,
D-Type (Phillip Eaton)
Home: +44 (0) 1536 268424
Work: +44 (0) 1536 760156
Mobile: +44 (0) 7775 726366
Fax: +44 (0) 870 055 4815
Email: phil@pjeaton.demon.co.uk
Website: http://www.pjeaton.demon.co.uk
