[Coco] Interfacing (was: Re: RS232 Schematics, was DriveWire survey)

[CoCoList for Color Computer Enthusiasts]

Changing the subject line, as per etiquette:

> That does sound good for compatibility. Would it mean throughput limited to
> traditional 6551 speeds?  Thats the only potential drawback I could see.
> Even the 1.x MHz coco craves data at rates in the (low) mbps range :)
No, throughput would not be limited.  remember, we're emulating the 
registers of the 6551, but not the speed of the 6551.  We can pull data 
from the data send register at the speed of the uC on the other side (If 
an AVR, that's multiple MHz).

The only trick is to emulate the registers well.

So, when the uC pulls a byte from the SEND register, it needs to set the 
SEND REG FULL bit in the status register to 0.  As well, when it stuffs 
a value in the RECV register, it needs to set the RECV REG FULL bit to 
1.  That's where the CPLD shines, as it can do those things automatically.

A simpler interface, like the Becker interface, is even easier...

Jim