Analog modem emulator?

Tony Duell ard at
Sat Aug 6 20:16:06 CDT 2005

> > 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.

Yep... I first came across it driving a Qume Sprint 5

> 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.


> Tim.

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