[Coco] Coco ProtoType Board
jdaggett at gate.net
jdaggett at gate.net
Sat Sep 2 14:52:05 EDT 2006
On 2 Sep 2006 at 12:11, Joel Ewy wrote:
> Mike Pepe wrote:
> > Hi James,
> >> 2) some form of flexible address decoding included along with
> >> buffering. It is still unclear as to whether just the Coco 3 I/O
> >> range be flexible or also the range from $C000 to $FFDF also be
> >> included.
> > I think the PLD would be nice, but overkill.
> If it's a 100-pin fine pitch SMT that only uses a few outputs and leaves
> the rest unconnected, has 150 registered macrocells that are permanently
> wasted, and takes the price right out of the impoverished CoCo hobbyist
> range, then I would concur with Mike that a few 74xx chips would be a
> better option.
in a 100 pin TQFP, Xilinx has 72, 108 and 144 macro cell devices. That is 1600,
2400, and 3200 gate equivalent devices. A XC9572 can do a simple 256 color
VGA video adaptor and use less 70% of the available resources.
Also to do all the data buss buffering and address decodeing, one will need about
50 I/O pins plus the JTAG pins.
> On the other hand, if the PLD can be re-programmed in situ, (I think at
> least some CPLDs can be??) then "overkill" here means "extra potential
> features". Certainly you don't need more than a few TTL chips just to
> decode some addresses. But if you can get more logic in the same space,
> and something approaching the same price, and if that logic can be
> appropriated by the user, then I would see it as worthwhile. If the thing
> could be made to mimic an MPI, for instance, or could be programmed with
> internal registers or counters, then it would be a significant improvement
> over a dedicated address decoder circuit. If the extra I/O lines were
> brought out to .1" headers, it would seem like useful potential, not
All CPLDs made today are in circuit programmable and are flash technology.
They boast 20 year data retention.
> A reasonable compromise, in the event that the PLD in question is not
> reprogrammable in circuit, would be to try to use up as much logic as
> possible on potentially useful functions, and make it available through
> jumpers or DIP switches, and MPI-like internal selection.
> Of course the main purpose of such a board would be for hobbyists to
> attach their own gadgets. But a simple expansion kit could turn it into
> an enhanced Multipak replacement for the less technically inclined. I
> have a CoCo 3 in a mini-tower case and have used a ribbon- Y-cable to hook
> up a Disto SC-II/4-in-one and an RS-232 pak. I'm not going to tear apart
> my one MPI to try to wedge the board in the mini-tower. I don't think it
> would fit anyway. But if I had an inexpensive project board that had MPI
> circuitry built-in, that would be another story. I would also burn
> several of my favorite cartridge games on a 27512 and stick that in one of
> the "slots". Wouldn't it be nice if the logic to switch banks in a larger
> EPROM would be built into such a device? I'm confident I could add that
> myself. I have the hardware and software (and I think, the knowledge) to
> program PALs and GALs. But if the capability is already present in a
> board I could purchase for, say, <$50, I would rather save myself the time
> and effort. And most CoCo hobbyists probably don't have a universal
> device programmer.
I have looked into a revamped MPI and expanded capabilites. There are
interesting potentials here.
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