[Coco] On John Linnville's Color Computer Game Master Cartridge Design

[go4retro at go4retro.com]

   After my initial result (non results), I went looking for some
   examples, since the IC is 40+ years old, and I figured there would be
   lots of designs. No joy there, as all the projects I see used a uC or
   Arduino to drive the unit. Then, I went to John's video, but it focuses
   on usage, not design.
   As Darren notes, your idea comprises the solution. It can all be put
   inside the CPLD, but that eats up 8 IO lines (for the latch output),
   which is precious. Keeping it as CPLD control IO and a separate latch
   probably makes more sense, but means yet another part to layout and
   stuff.
   The AY is dirt easy in relation.
   Jim
   > On August 2, 2017 at 2:39 PM Zippster <zippster278 at gmail.com> wrote:
   >
   >
   > Hmm, was not aware of that. I haven't seen any details of the design.
   >
   > Easy enough to handle with some modern programmable logic in the
   loop, but it sounds like john didn't use any.
   > A latch in combination with the ready pin and programming technique
   would do with old school components I suppose
   > from the sound of it, though I haven't really looked at that data
   sheet.
   >
   > - Ed
   >
   >
   > > On Aug 2, 2017, at 1:23 PM, RETRO Innovations
   <go4retro at go4retro.com> wrote:
   > >
   > > At CocoFEST, John and I discussed potential additional
   opportunities for the SN76489 sound IC within the Coco community. After
   recovering from the fest, I ordered a batch of the ICs and I sent out a
   PCB design to attach the unit to a Coco. While the boards arrived many
   weeks back, I have been busy with other things and, as discussed on
   both the podcast and CocoTALK, I've been a bit unmotivated to finish
   the design.
   > >
   > > Well, I decided I should at least get the unit working, so I would
   at least be knowledgeable about the IC and its capabilities. The
   datasheet specifies a quite lengthy cycle time needed to store data
   into the unit, but I was undeterred.
   > >
   > > And, after 3 nights working (fighting) with this IC, I think people
   should give more credit to John for his design. He didn't just wire up
   this IC to the Coco expansion bus, he performed some magic to
   successfully map it into the Coco address range.
   > >
   > > The SN76489 takes 32 4MHz cycles to successfully store a value in a
   register, which is 8uS, though that might be worst case, as I see 3uS
   typical. In any event, this need to hold the data valid for so long
   makes a simple connection to the Coco bus more complex (essentially,
   unless one wants to HALT the CPU while the write completes, it appears
   one needs to store the data in a faster "buffer register" and then hold
   the bus signals to the IC until the IC signals the write is complete
   (there is a "READY" pin)).
   > >
   > > I thought I'd point this out, since I originally did not have a
   full appreciation for John's accomplishment. As it stands, my original
   PCB won't work, but I was able to verify correct operation by attaching
   the IC to a microcontroller and successfully pushing sound out of it
   that way (I know the chips are good).
   > >
   > > Jim
   > >
   > > --
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   > >
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