[Coco] bitbanger I/O

[Neil Morrison]

IIRC, the CD line goes and stays high if the printer is not busy. This is 
for the TP-10 :-
2. STATUS (Pin No.2)

Direction - To Computer
This signal indicates to the computer whether or not the Printer can accept 
data. The OFF condition (LOW) indicates that the Printer is BUSY and cannot 
accept any more data. The ON condition (HIGH) indicates the printer is NOT 
BUSY, and can accept more data from the Computer. This line goes LOW (BUSY) 
while:

  1.. One-code ASCII data is received.
  2.. Power-up is initialized.
  3.. The PAPER FEED Key is pressed and data is received.
  4.. Paper is jammed so that the Printer cannot shift the print head.
  5.. Executing the Self Test Printing.
Neil

----- Original Message ----- 
From: "Roger Taylor" <webmaster at coco3.com>


> 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.