Printer (parallel) port buffering direction
Posted: 30 Apr 2026 14:30
I have an old "ST Applications" article (issue 2, January 1991) entitled "ST parallel port buffer" which I thought would be useful to have in my STe. It's a rather basic circuit involving a 74HCT245 for buffering the 8 data lines (D0 to D7) while the STROBE line is buffered by a transistor. So far so good.
The limitation is that this is only good for output. That's fine for most common uses (output to a printer), but I suppose there are instances where you'd want to use the parallel port as an input (a MIDI expansion device perhaps, such as the Soundpool MO-4 or Friend Chip MM-1 (Sound On Sound link) and (Atari74User link), both boxes intended for Cubase).
EDIT: strike the above! I just realized that these boxes only give additonal MIDI ouputs and no inputs. So a question arises: in which situation/which hardware would be attached to the ST's printer port where you'd input (or both input and output) something? The magazine article did mention that it only handles output unless modified, so there must be some use of that port being used as an input.
I'm aware that the buffer circuit can easily have its direction reversed by pulling the 74HCT245 DIR (pin 1) to VCC, but how would I go about to having this done automatically without the need for a switch (i.e. the parallel port behaving in the same way as without the buffer add-on)?
Attached is the mentioned "ST Applications" article.
(Unfortunately I didn't scan the whole magazine while I had it, and I can't seem to find that particular issue anywhere online).
The limitation is that this is only good for output. That's fine for most common uses (output to a printer), but I suppose there are instances where you'd want to use the parallel port as an input (a MIDI expansion device perhaps, such as the Soundpool MO-4 or Friend Chip MM-1 (Sound On Sound link) and (Atari74User link), both boxes intended for Cubase).
EDIT: strike the above! I just realized that these boxes only give additonal MIDI ouputs and no inputs. So a question arises: in which situation/which hardware would be attached to the ST's printer port where you'd input (or both input and output) something? The magazine article did mention that it only handles output unless modified, so there must be some use of that port being used as an input.
I'm aware that the buffer circuit can easily have its direction reversed by pulling the 74HCT245 DIR (pin 1) to VCC, but how would I go about to having this done automatically without the need for a switch (i.e. the parallel port behaving in the same way as without the buffer add-on)?
Attached is the mentioned "ST Applications" article.
(Unfortunately I didn't scan the whole magazine while I had it, and I can't seem to find that particular issue anywhere online).