Comment by YZF

Comment by YZF 10 months ago

A standard PC parallel port does not provide interrupts on data lines.

The difference is more that you can control those output lines with really low latency and guaranteed timing. USB has a protocol layer that is less deterministic. So if you need to generate a step signal for a stepper motor e.g. you can bit bang it a lot more accurately through a direct parallel port than a USB to parallel adapter (which is really designed for printing through USB and has very different set of requirements).

cwillu 10 months ago

Are you sure about that? I'd have bet money that the input lines have an interrupt assigned, and googling seems to agree.

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YZF 10 months ago

I used the parallel port extensively. I've had the IBM PC AT Technical Reference that had a complete reference to the parallel port. I've read it many times.
But alas, it was decades ago, so it's possible I'm wrong ;)
This is the closest reference I can find: https://www.sfu.ca/phys/430/datasheets/parport.html
The card does have an interrupt but only the ACK signal can interrupt. Not the Data lines. ACK makes sense since it would be part of the printing protocol, you'd send another byte each interrupt.

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