Parallel Port Does Not Work in Input Mode

kagouraki wrote:

Found the problem... i have this chinese break out board with the 17 optocouplers(one on each pin). They are onedirectional... so... 60 euros wasted... Another question. Does anyone know what is the logic level of the parallel port and how safe is to connect direct all my input to the parallel port without breakout board?
i have only switches and one encoder. no motors relays etc. Thank you..

If your BOB is a DB25-1205 with the 17 optocouplers, we tested it on the bench with a multimeter and 5 v power supply (no PC) on the weekend and confirmed that it works on both inputs and outputs. Eg. All pins show a voltage in them by default and they are active low so 0V is on. Grounding one of the BOB inputs drops the 5 v on the corresponding DB25 pin. Grounding one of the DB25 connector output pins, drops the voltage on the BOB output. In our case, a faulty riser cable from the motherboard was the problem. This is how I diagnosed the faulty cable. Replacing it got the BOB working properly

I found that because the input pins in the BOB end of the cable are mostly in line with the ground pins, it is easy to test the PC side of it with the BOB removed and shorting the cable input pins to a ground pin with a screwdriver. You should be able to monitor the change of state using Axis tools. I would do this first so you know the parallel port is actually working.

There is an option to run isolated power so it may be possible to run 3.3v on the PC side and 5v on the BOB side by removing the 2 links. You may need to put one of the links on the third unpopulated link so experiment without the PC connected.

I'm pretty sure the question was about using the parallel port in "in-mode" and using pins 2-9 as inputs, and that breakout board can't do it. You have to buy a breakout board that is set up for bi-directional. Such as a C10.
cnc4pc.com/motion-control/breakout-board...-interface-card.html