Path: utzoo!attcan!uunet!ncrlnk!ncrcae!hubcap!gatech!purdue!decwrl!pyramid!prls!philabs!pwa-b!hgcvax!network
From: network@hgcvax.uucp (craig chaiken)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Using the printer port for input
Summary: Parallel Port as input port
Message-ID: <691@hgcvax.uucp>
Date: 13 Jan 89 05:21:40 GMT
References: <704@krafla.rhi.hi.is>
Organization: Hartford Graduate Center, Hatrford, CT.
Lines: 33

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. 
> 
> My question is: Does anyone have a code fragment (in C, assembler or
> whatever) for changing the port into an input port?
> 
(*** The following is an except of my, soon to be published book,    ***)
(*** _Blueprint of a Local Area Network_.  It soon be available from ***)
(*** M & T Publishing for $24.95 sometime around July.  The book     ***)
(*** provides the source code and details the hardware necessary to  ***)
(*** build an inexpensive, customized IBM PC Local Area network.     ***)
(*** Both hardware hackers an assembly language programmers, alike   ***)
(*** will find that it is chock full of useful information, and      ***)
(*** techniques.                                                     ***)

     The parallel port on the IBM PC was designed for use with a parallel
printer.  It provides 8 output-only lines, mapped to bits 0 through 7 of
I/O port 0378H, which are data bit 0 through data bit 7.  It provides 5
input-only lines. mapped to bits 3 through 7 of I/O port 0379H, which are
ERROR, SELECT, PAPER_END, ACKNOWLEDGE, and BUSY.  And it provides 4
input/output lines, mapped to bits 0 through 3 of I/O port 037AH, which
are STROBE, AUTO_LINE_FEED, INITIALIZE, and SELECT_IN (* Note -
in order to input from this port, you must first send 04H to I/O port
037AH *).  BUSY, AUTO_LINE_FEED, and STROBE input signals are inverted by
the hardware, and must be negated in software.

(*** End of Excerpt from Blueprint of a Local Area Network ***)

Craig Chaiken
Hartford Graduate Center
Computing Services