[Coco] MCI

[RETRO Innovations]

On 8/30/2016 10:02 AM, Camillus_gmail wrote:
> Hi Jim,
>
>
> What is the status of your 8 port MCI, any progress?
>
> Thanks
>
> cb
>

At the show, John Mark provided a nice suggestion for the design of 
additional ports, and I am considering adding it.


His suggestion was that ports above 4 be much more isolated from the bus 
than ports 1-4.  Namely, for ports 5+, if the port is not selected, the 
card would not see any address or data activity (maybe tie the address 
lines to all 1 and read to 1, but leave the clocks there in case the 
unit needed long term timing. hold SCS and CART at 1 as well).  SLENB 
and other cart outputs should be OK unbuffered, but buffered should not 
hurt them.

I like the idea because the Coco peripheral space has some serious 
challenges.  Cards that don't honor SCS, some that overstep their 
address spaces, etc.

Since I have a bit of extra room in the CPLD, it's easy to add there.  
The ~32 bits of buffering I need per port might be a bit non trivial, though



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