Also, the easiest way to build the cable to connect the parallel port to your prototype on the breadboard is getting a standard parallel printer cable and cutting the Centronics connector from it. After that, you will need to find out where each wire is connected. With a multitester on resistance (or continuity) scale, put one of the probes on the wire you are trying to find out its function and test the other probe on each pin of the 25-pin connector of the cable. When the resistance goes to zero (or the multitester beeps, if you are using its continuity scale), you found which pin on the 25-pin connector that particular wire is connected to. Label that wire with the pin function (so you won’t need to go all through this process again) and go to the next wire, until you have found the function for every wire on the cable.

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Figure 6: A close-up on our breadboard unit. See how we labeled the wires.

Regarding the pin numbering, pay close attention to the 25-pin plug and you will see that each pin is numbered, see Figure 7.

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Figure 7: A close-up on the 25-pin connector, see how each pin is numbered.

After you assembled your circuit, it is time to put it to work.