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From: grege@gold.gvg.tek.com (Greg Ebert)
Newsgroups: sci.electronics
Subject: Re: A/D converter ==> PC parallel port?
Keywords: A/D parallel port
Message-ID: <1793@gold.gvg.tek.com>
Date: 12 Dec 90 22:21:45 GMT
References: <billq.661025394@s.ms.uky.edu>
Distribution: sci.electronics
Organization: Grass Valley Group, Grass Valley, CA
Lines: 26


In order to read-in through a PC's parallel port, you need to either:

	(1) Disable (ie, tristate) the output driver. If your card
	uses an ASIC, it might be difficult. I think the 16452 from
	VLSI Technology has an output-enable function.

	If there is a genuine 74xx374, you can put a switch on the OE
	pin. I would be very cautious about using an unused bit on the
	control port to drive OE because some wacko software [about 99%
	of what's out there :-{ ] might disable your port.

	(2) Or, 'backdrive' the output driver. Try writing 'FF' to the data
	port (278h, 378h, or 3BCh) and use a beefy driver to yank-down
	the lines. Be careful, because there are several types of RC filter
	topologies for slew-rate/spike protection; if the readback buffer
	is *between* the resistor and the port connector pin, you might
	have some trouble.

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