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Parallel Port Loop back bits 5-7

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  • David (PassMark)
    The parallel port was never designed for data input (I am refering to the early PC days here). You could output 8 bits to the printer and get back very limited information from the printer (like a signal to indicate 'out of paper').

    So the early parallel ports only had 5 useable inputs (not enough to make a 8 bit byte).

    So if we made parallel loop back plugs to test 8 input and output pins it would fail on older PCs.

    Most new PCs are now using USB instead of parallel ports. So we need to be compatible with old PCs (becuase they are the ones with parallel ports).


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  • REM
    started a topic Parallel Port Loop back bits 5-7

    Parallel Port Loop back bits 5-7

    I'm using BurnIn Test 4.0 and testing 1 parrallel, 2 serial ports on a docking station.

    After looking at you literture on the wiring of the loop back connectors, I'm wondering why data bits 5-7 are not tested on the parallel port and what would be the reason for that?

    The system I'm testing uses the parrallel port for either a printer or an external floppy drive, which requires all 8 data bits.

    So far I haven't had a problem, but if there is a problem of with the internal connections of the dock with data bits 5-7 of the port then the BurnIn Test would not catch the problem.

    I would like to know if there is a different Loop Back plug that would test these bits?