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I have a 20 year old device that prints data through a 1994 HP Deskjet 550c printer using a parallel port. Now the printer is broken and so there's no way to view the device output. I was thinking of hooking the parallel port from the device to a Raspberry Pi 3 which will display the data on a computer screen. I can get a parallel to USB cable which connects the old device to the Raspberry Pi. When I press the print button on the device, data should be sent to the Pi, but what I'm worried about is the format of the data. Is there a standard protocol for print data, or does every printer manufacturer use their own protocol? Do you know of any open sourced python scripts that can directly parse the print data coming from the usb port? Do I need to install any drivers on the Pi?

user3528623
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    In addition to the parallel to USB cable, I think you will need a "null printer" or [LapLink](https://en.wikipedia.org/wiki/LapLink_cable) cable since the RPi is on the receiving end of the data pretending to be the printer. You might have to set some bits like [`ack`, `busy`, and `error`](https://en.wikipedia.org/wiki/Parallel_port) to the appropriate hi/lo levels to make the device believe the RPi is a printer, and that you are ready to receive data. Very interesting project! – jamieguinan Mar 04 '16 at 22:17
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    As for the protocol, I'm guessing that printer used some flavor of HP PCL and not PostScript. Once you start reading data, this project called [OpenPCL](http://openpcl.sourceforge.net/) might be useful to interepret and display it. – jamieguinan Mar 04 '16 at 22:21

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