[Coco] bitbanger I/O

[Roger Taylor]

I'm trying to refresh my memory on how the bitbanger CD line works when 
receiving serial data (not a printer).

I assume that a FIRQ can be generated at the beginning of each incoming 
byte if the CD line is connected to the sending device's RTS or some other 
line that indicates that a byte is on the way.

I found some popular source code for Disk BASIC assembly for receiving at 
38400bps over the bitbanger port but it doesn't use the CD line as far as I 
can tell.  I wonder how easy it is to get off-sync even though it watches 
carefully for the start bit.  The program masks interrupts during the byte 
receive portion of the code.

I want to make my CoCo to PC cable compatible with OS-9, but I'm not sure 
if OS-9 can handle masking the IRQ interrupts while receiving a byte then 
restoring the interrupts and not cause problems elsewhere in OS-9 like lockups.





-- 
Roger Taylor