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Article #5097Re: Is PC parallel port latched?
From: Mark Zenier
Date: Sun, 15 Jul 1990 19:50
Date: Sun, 15 Jul 1990 19:50
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In article <15568@ucsd.Edu>, brian@ucsd.Edu (Brian Kantor) writes: > The IBM technical reference manual shows an LS374 in there, which is an > 8-bit latch. The data lines are latched, but there's an LS244 reading > them back in when you read from the port so that you can perform a > self-test by reading back the byte you had just output. > > Thus you can make the port bi-directional if you want. Just chop the > wire from the latch's output enable pin, and run it out to a spare pin > on the connector. The external device would control the direction. In a old TTL implementation, you can also route the output enable to an unused bit in the control register. This is a configuration jumper on some boards. There was a article 2-3 years ago in Computer Shopper giving the gory details. Markz@ssc.uucp
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!pilchuck!ssc!markz From: markz@ssc.UUCP (Mark Zenier) Newsgroups: sci.electronics Subject: Re: Is PC parallel port latched? Message-ID: <905@ssc.UUCP> Date: 15 Jul 90 19:50:25 GMT References: <33965@ut-emx.UUCP> <1990Jul15.014354.12657@ux1.cso.uiuc.edu> <15568@ucsd.Edu> Organization: SSC, Inc., Seattle, WA Lines: 16