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From: dougs@tvnews.tv.tek.com (Doug Stevens)
Newsgroups: alt.msdos.programmer,comp.os.msdos.programmer
Subject: Re: Programming the printer port to read in data.
Message-ID: <1991May22.233318.11680@tvnews.tv.tek.com>
Date: 22 May 91 23:33:18 GMT
Article-I.D.: tvnews.1991May22.233318.11680
References: <1991May21.202043.24725@magnus.acs.ohio-state.edu> <1991May22.104513.22169@msuinfo.cl.msu.edu>
Distribution: usa
Organization: Tektronix TV Measurement Systems, Beaverton, OR
Lines: 34

It seems that it is not generally known that each printer port contains
three registers (some cheapo printer cards only implement two). 

The register at offset 0 from the I/O location of the printer is write-only,
for data (there is a diagnostic read-back, which is the same as what was
written if the card is working properly).

The register at offset 1 contains:

	Bit		Fxn
	---		---
	7		Busy			(~read)
	6		Ack			(read)
	5		Out of paper		(read)
	4		Printer selected	(read)
	3		Error			
	2		IRQ occurred		(read)
	1-0		Reserved		(read)

The register at offset 2 contains:

	Bit		Fxn
	---		---
	7-5		Reserved
	4		Enable IRQ
	3		Select printer		(~read, ~write)
	2		Init printer		(read, ~write)
	1		Auto LF			(~read, ~write)
	0		Strobe			(~read, ~write)

I think that it is at offset 2 that you must write all 1's to the port
before you can use it to read.

There may be typo's here -- caveat emptor!