Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!ncar!husc6!cs.utexas.edu!ut-emx!nather
From: nather@ut-emx.UUCP (Ed Nather)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Using the printer port for input
Message-ID: <9439@ut-emx.UUCP>
Date: 14 Jan 89 16:48:27 GMT
References: <704@krafla.rhi.hi.is> <816@ttrde.UUCP>
Organization: The University of Texas at Austin, Austin, Texas
Lines: 26

In article <816@ttrde.UUCP>, pfales@ttrde.UUCP (Peter Fales) writes:
> In article <704@krafla.rhi.hi.is>, frisk@rhi.hi.is (Fridrik Skulason) writes:
> > I need to connect a set of eight switches to my PC. The most simple way 
> > to do it seems to be connecting them to the parallel port, and using it
> > as input port instead of output. 
> > 
> 
> Sorry, the standard PC parallel port hardware is not capable of being
> used as an input port no matter how clever your code is.  
> 

I'm glad I didn't know this when I wrote my "portfinder" routine, which
finds the port name of the printer port -- you have to put a dummy plug
in, which the program looks for.  It does this by sending out 4-bit
codes, then reading the various possible ports to see if it can find the
code -- by using lines in the output port as input bits.  As I recall
(it's been several years) I could only input 4 bit codes, not 8 bit --
there weren't enough input lines for 8 of them.  I did the input in
two-nibble bytes.


"`Impossible' is a challenge, not a truth."

-- 
Ed Nather
Astronomy Dept, U of Texas @ Austin