6 Aug
2005
6 Aug
'05
6:16 p.m.
The Apple Serial Card I have doesn't have any
UART, or shift
registers, or anything like that. Just a few TTL chips to make
a 1 bit I/O port [...]
This card was used mainly (but not exclusively!) to drive serial
printers. I think the firmware is expressly half-duplex.
A far more common and useful card is the slightly later "Super
Serial" which has a 6551 UART IIRC.
Correct. I am not sure it's more common over here, though. I must have 3
or 4 of the bit-bangers, one Super Serial card and a number of 3rd party
cards based on the 6850 or 6551. Some of the latter also had parallel
ports (6821-based).
I think there may have been a revision to the original
UARTless
serial card's firmware that allowed it to detect flow-control
characters from the printer (e.g. XON/XOFF) even though it
was half-duplex.
The P8A PROM IIRC. You lost the block-transfer operations (which nobody
ever used...). It wasn't XON/XOFF, it was ETX/ACK or something, though.
It was certainly required for using the card with that Sprint 5.
-tony
Tim.