[Coco] 6551 at 115200 bps

[Roger Taylor]

Has anyone noticed on Sock's website he mentions that doubling the 
6551 crystal value to 3.6864 mhz can be done but setting the 6551 to 
the ExternalClock/16 mode would yield 115200 bps, then he says:  " 
this *almost* works! "   Why wouldn't it work?

We've proven that the CoCo can send and receive through the BITBANGER 
port at 115.2 bps, and believe it or not - 230.4 kbps.

Maybe Sock means that IRQ can't be triggered that fast and the CoCo 
keep up?  Why not?  The 6551's IRQ goes to the CART signal which is 
tied to FIRQ.  A circular buffer in the FIRQ service routine could do 
a quick FIFO store to a buffer and it should work?  If not, the 
crystal should probably be dropped to 1.8432 / 2  to yield a 57600 
bps mode which should work.
-- 
Roger Taylor

http://www.wordofthedayonline.com