[TriLUG] Line Printer Terminal

Ed Hill ed at eh3.com
Mon Apr 17 16:48:05 EDT 2006

On Mon, 2006-04-17 at 15:23 -0500, Gaurav Gupta wrote:
> I am trying to read/write data from/to the line printer terminal of my laptop.
> I used the c program available at
> http://www.epanorama.net/circuits/parallel_output.html#linuxprogramming
> When I write some data to the data register of the printer port and
> try to read it back I see the correct result. But the when I
> physically check the pins of the printer port they don't show the
> correct data.
> I used the base address for the data register as 0x378 (an
> introduction is available at
> http://www.logix4u.net/parallelport1.htm). Can someone tell where I
> could have gone wrong? Maybe the base address on my laptop is
> different. My laptop is hp zt3000 model and is running gentoo.
> Will appreciate any suggestions.

Hi Gaurav,

Its been years since I've done any serial or parallel port coding but
here are some quick things to check in no particular order:

 - have you made sure that the parallel port is enabled in the BIOS
   (some machines have BIOS defaults that turn off the parallel 
   and/or serial ports by default)

 - have you looked at some of the helpful FAQs that describe the 
   parallel port pin-outs, voltages, etc. 


   and convinced yourself that you have a real no-signal problem 

 - can you get some sort of software "snooper" or perhaps a plug-in 
   device that shows (or, even better, logs) what is happening over 
   the parallel port?

 - supposedly, its easy to damage a parallel port through accidental 
   grounding -- are certain that you have a fully functional and
   undamaged parallel port?  can you check behavior on another 
   machine?  or, do you have a different program that you could use  
   to verify that the port is working (like, plug a printer into it 
   and see if things can be printed!)


Edward H. Hill III, PhD
office:  MIT Dept. of EAPS;  Rm 54-1424;  77 Massachusetts Ave.
             Cambridge, MA 02139-4307
emails:  eh3 at mit.edu                ed at eh3.com
URLs:    http://web.mit.edu/eh3/    http://eh3.com/
phone:   617-253-0098
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