[Coco] RS232 Schematics, was DriveWire survey

[CoCoList for Color Computer Enthusiasts]

On Sun, May 11, 2014 at 11:27 PM, CoCoList for Color Computer Enthusiasts <
coco at maltedmedia.com> wrote:

>
> Could you use something like a UPB8216C to do it? I found a couple in a
> grab bag I got from Jameco and I set them aside thinking they might be
> useful to allow an Arduino/Pi to communicate over the bus with some retro
> computer.
>
> http://www.datasheetlib.com/datasheet/1004516/upb8216c_nec-electronics.html
>
> FozzTexx
>

FozzTexx,

Signal level and buffering is important, but that's not really the big
problem.  My little bus buffer board essentially does that part with a
couple of wide chips.  The bigger problem is signal timing - the Coco wants
to access bus objects like memory, and that means with memory timing.  If
you take a look at the CPI data sheet, a read is fairly tight - it puts the
address on the address bus, and it expects to be able to read the data only
a short time later.  The timing is tight enough that with a standard AVR
chip I determined that I wouldn't even have time to get into the interrupt
routine on the AVR in most cases.  It's a fun little problem.
  -Matt