Author Topic: Parallel Port Hardware - Currents and Voltages  (Read 18430 times)


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Parallel Port Hardware - Currents and Voltages
« on: December 11, 2010, 11:55:35 am »
I am developing an input/output device using parallel port and logix4u's inpout.dll  ;D

Im using WinXP.. the software side is good under =)

But I am having a hard time searching the net about the hardware side.

I need more info's about it because I am really interested. ::)

What is the voltage and current produced by the outputs?
What is the voltage and current required by the inputs?

Making a mistake will harm my system.. ???

- - - -

Another topic.. :D

We know that new printers supports usb instead of parallel ports.

I want to use a parallel to usb adapter because usb ports are everywhere :P

can I use the usb instead to produce the same output as parallel ports?  ;D


Jan Axelson

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Re: Parallel Port Hardware - Currents and Voltages
« Reply #1 on: December 11, 2010, 03:29:51 pm »
From my FAQ at:

The data outputs on the original parallel port were 74LS374 outputs, which can source 2.6 milliamps at 2.4 guaranteed, 3.1V typical. The data outputs on most parallel ports are at least as strong as the original port's, but no guarantees. If you need 5V, you can use one of the high-efficiency step-up regulators from Maxim & others (Max756). The newer port controller chips often have IEEE-1284 Level 2 outputs, which can source 12 milliamps at 2.5V. The Control outputs were originally open-collector TTL with 4.7K pullups, so these are less useful as current sources.


Most commercial USB/parallel=port adapters identify themselves to the host computer as printers and thus only work with printers.

For other parallel-port devices, see:

Converter From USB To Parallel from Henrik Haftmann

Many USB development boards provide I/O bits and host software to control them.

Jan Axelson
« Last Edit: June 27, 2015, 09:44:04 am by Jan Axelson »