[Coco] MPI (was Re: A new idea for a CoCoSDC expander)

[RETRO Innovations]

On 10/15/2014 11:58 AM, Kandur wrote:
> CPLD would be the right way to go, if the TTL stuff would fit in it.
> IMHO very few people need to plug in 8 cartridges at once.
> Adding a MAX-232 chip would come handy for the Coco 2 and 3s
> providing RS-232 signals, then we could power it with a simple 5V wall-wart.
>
> Kandur
>
I'll be honest, I am very interested in doing a design, if for nothing 
else, just to understand how the unit works.  I'd prefer to take the 
daughtercard of John's design and marry it up to Gunnison's design, but 
his design is very hard to follow.  I think it'd be easier to design 
something from scratch, but I'm new to the community, and I am not sure 
I understand all of what the unit does.

  * It looks like it allows hardware selection of 1 of 4 slots by
    switching the SCS, CART, and CTS lines.
      o Any other lines switched?
  * It looks like it buffers the Address and Data lines
      o Any other lines buffered?
  * It has a memory register to switch the cart part under SW control
      o I assume the register will show which cart port has been
        selected, and allow one to override the switches.
      o If I am correct, and someone selects another port via SW, do the
        switches allow one to override the SW selection?
  * Some LEDS
  * a switch for cart autostart

Is there a document that describes what the unit does, without talking 
about the schematic per se?

Jim



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