Making data pins in parallel port bi-directional,

Thread Starter


Joined Nov 10, 2009
I have been working on a project to measure temperature using LM 35 sensor the main problem i am facing is that the data or output pins of the parallel port have to be used to read data instead of writing. Can anyone tell how can i make data pins able to read data as well?


Joined May 11, 2009
I agree with CDRIVE. Can you tell us more about your project? A micro -controller with ADC+UART and some MAX323 type level converter is all you need. Maybe an additional opamp, for the LM35. The rest is programming only.


Joined Sep 26, 2009
Most Parallel ports are can not have bi directional data lines unless it supports it, most of the time manufacturers of motherboards will not add bidirectional functionality to maximize use of board space and all, but a standard Parallel port does have atleast 5 pins you can read as inputs, those are normally the control lines for Paper Out, Online, Etc...

I attached a pic of the parallel port pins and functions.....
PORT refers to the physical address of the parallel port (i.e. &H378, etc.)

My .02



Joined Oct 17, 2009
i didn't think the data lines were bi-directional.

It would be best using something like a 74150 to extend the four input lines. You could extent the inputs to more than 32 inputs with still enough outputs to control various actuators, etc.

Remember, you have the control lines too, so you have 12 outputs in total to use and four inputs.