[Coco] RS232 Schematics, was DriveWire survey

[CoCoList for Color Computer Enthusiasts]

On Sun, May 11, 2014 at 9:30 PM, CoCoList for Color Computer Enthusiasts
wrote:

>
> I ran into the same issue.  The solution I found was to use a CPLD as a
> dual-interface memory between the Coco bus and the uC.  The CPLD can be
> clocked fast such that each device thinks it has exclusive access to the
> register.  A write from the Coco side triggers an interrupt on the uC
> side.  You could do the reverse as well if NMI was available.  If not,
> having the Coco device driver poll a status register would work.
>


I would agree that a CPLD is probably the best way to go.  For the CoCo SDC
I used a CPLD to implement a dual port register file that can be accessed
in parallel by both the CoCo and the AVR uC. There is also some simple
handshaking logic to allow coordinated transfers with almost no overhead.
On a CoCo with a 6309, it allows me to use the TFM instruction to do block
transfers to and from the AVR at the highest possible speed (without
resorting to DMA).

Darren