3 ms·

Bear in mind that this will work for many bits of parallel port equipment, but won't work for everything. Some things use very precisely timed signals, as shor

Bear in mind that this will work for many bits of parallel port equipment, but won't work for everything. Some things use very precisely timed signals, as short as a few microseconds, and that simply can't be recreated by software over USB without hardware support.

blueflow 4y ago
The parallel printing protocol is synchronous in both directions. Both the Computer and the Printer will wait on each other. Edit: s/port/printing/
- pifm_guy 4y ago
  But not everything uses that. Some software simply connects a pin of the port to a motor and another to a sensor, then uses software in the computer to turn the motor off as soon as it sees the sensor be activated. Devices that do that often have very tight timing requirements - since original 1990's era computers could respond to a change in a pin change in as little as a few clock cycles.
  - zozbot234 4y ago
    This. The parallel port is pretty much the original GPIO.
  - deleted 4y ago
    [deleted]
- akiselev 4y ago
  It’s synchronous but it was offloaded on to the southbridge in Intel/AMD CPUs so you could fill a ring buffer and it’d DMA everything to the peripheral without interrupting the CPU. Drivers could just leisurely fill up those ring buffers and never have to worry about kernel scheduling inhibiting hard realtime. As an input the interrupt could also drop into a driver much faster than userland software. CNCs with MachCNC software and lots of old industrial equipment operated this way since it saved money on custom PCB designs. BART [1] still buys older motherboards with parallel ports wired to the south bridge because USB adaptors can’t guarantee timing and swapping to a PCIe card would require rewriting some old stuff. However it has to be done at the driver level, it wasn’t Postscript or GCode or something like that, so I doubt this piece of gear will be anywhere as useful as parallel ports used to be. [1] https://news.ycombinator.com/item?id=32884814 https://news.ycombinator.com/item?id=32884814
- memcg 4y ago
  I remember trying to interface a PCs Limited (original Dell) parallel port to a Slo Syn paper tape reader on Excellon PCB drills and routers around 1995.
Goz3rr 4y ago
Doesn't this device work the other way around? It's pretending to be a printer, which you can connect to an old computer that expects to see a printer on its parallel port. What you're describing sounds more relevant for something that's adding a parallel port to a modern computer?
- a2tech 4y ago
  From looking at the comments on here it seems many people are missing the point of this device and are thinking of it as something more than what it is--which is an adapter from an old device to a modern printer. It is not a general replacement for 2-way parallel port communication.
  - rwap 4y ago
    True - it is not designed for 2 way parallel port communication - it just captures the data sent to a parallel port and emulates an old printer (Epson ESC/P, ESC/P2, HP PCL, PostScript, Printronix, Tandy, IBM ProPrinter) - converting the output to PDF which can then be printed or stored. It was quite a bit later in the history of the printer, when equipment started to expect 2-way communication with printers - obtaining information about the model, ink levels, paper status etc - generally that type of equipment had printer drivers for each model of printer. We would have liked to implement something along those lines, but there is very little information (if any) about the status messages passed from the printer back to the equipment (it is not covered in the ESC/P2 documentation for example as that was last updated in 1990).

blueflow 4y ago

The parallel printing protocol is synchronous in both directions. Both the Computer and the Printer will wait on each other. Edit: s/port/printing/

pifm_guy 4y ago
But not everything uses that. Some software simply connects a pin of the port to a motor and another to a sensor, then uses software in the computer to turn the motor off as soon as it sees the sensor be activated. Devices that do that often have very tight timing requirements - since original 1990's era computers could respond to a change in a pin change in as little as a few clock cycles.
- zozbot234 4y ago
  This. The parallel port is pretty much the original GPIO.
- deleted 4y ago
  [deleted]
akiselev 4y ago
It’s synchronous but it was offloaded on to the southbridge in Intel/AMD CPUs so you could fill a ring buffer and it’d DMA everything to the peripheral without interrupting the CPU. Drivers could just leisurely fill up those ring buffers and never have to worry about kernel scheduling inhibiting hard realtime. As an input the interrupt could also drop into a driver much faster than userland software. CNCs with MachCNC software and lots of old industrial equipment operated this way since it saved money on custom PCB designs. BART [1] still buys older motherboards with parallel ports wired to the south bridge because USB adaptors can’t guarantee timing and swapping to a PCIe card would require rewriting some old stuff. However it has to be done at the driver level, it wasn’t Postscript or GCode or something like that, so I doubt this piece of gear will be anywhere as useful as parallel ports used to be. [1] https://news.ycombinator.com/item?id=32884814 https://news.ycombinator.com/item?id=32884814
memcg 4y ago
I remember trying to interface a PCs Limited (original Dell) parallel port to a Slo Syn paper tape reader on Excellon PCB drills and routers around 1995.

Goz3rr 4y ago

Doesn't this device work the other way around? It's pretending to be a printer, which you can connect to an old computer that expects to see a printer on its parallel port. What you're describing sounds more relevant for something that's adding a parallel port to a modern computer?

a2tech 4y ago
From looking at the comments on here it seems many people are missing the point of this device and are thinking of it as something more than what it is--which is an adapter from an old device to a modern printer. It is not a general replacement for 2-way parallel port communication.
- rwap 4y ago
  True - it is not designed for 2 way parallel port communication - it just captures the data sent to a parallel port and emulates an old printer (Epson ESC/P, ESC/P2, HP PCL, PostScript, Printronix, Tandy, IBM ProPrinter) - converting the output to PDF which can then be printed or stored. It was quite a bit later in the history of the printer, when equipment started to expect 2-way communication with printers - obtaining information about the model, ink levels, paper status etc - generally that type of equipment had printer drivers for each model of printer. We would have liked to implement something along those lines, but there is very little information (if any) about the status messages passed from the printer back to the equipment (it is not covered in the ESC/P2 documentation for example as that was last updated in 1990).