Re: LPT3 support

Article View: comp.sys.ibm.pc

Article #14876

#14876

From: John R. Levine
Date: Wed, 17 Dec 1986 15:24

13 lines
1521 bytes

The problem with the PC's printer interrupt is quite simple.  After you print
a character, the printer sends back a 5us ACK pulse to say it's ready for
another character.  The interrupt request is generated from that pulse.  If
your PC has its interrupts masked during those 5us, or if it takes longer than
5us for the instruction that's executing to finish, you lose the interrupt.
Had the guys at IBM who designed the interface been allowed to speak to the
people who bought the printers, they would probably have decided to generate
the interrupt from the not-busy line which stays up until you send the next
character, and which other machines with working printer interrupts use.  Pfui.
-- 
John R. Levine, Javelin Software Corp., Cambridge MA +1 617 494 1400
{ ihnp4 | decvax | cbosgd | harvard | yale }!ima!johnl, Levine@YALE.EDU
Where is Richard Nixon now that we need him?

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References: <133@parcvax.Xerox.COM> <295@ima.UUCP> <1348@cit-vax.Caltech.Edu>

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Path: arc1-ca.pugleaf.net!utzoo!mnetor!seismo!rutgers!mit-eddie!genrad!decvax!ima!johnl
From: johnl@ima.UUCP (John R. Levine)
Newsgroups: comp.sys.ibm.pc
Subject: Re: LPT3 support
Message-ID: <380@ima.UUCP>
Date: Wed, 17-Dec-86 10:24:27 EST
Article-I.D.: ima.380
Posted: Wed Dec 17 10:24:27 1986
Date-Received: Thu, 18-Dec-86 02:39:58 EST
References: <133@parcvax.Xerox.COM> <295@ima.UUCP> <1348@cit-vax.Caltech.Edu>
Reply-To: johnl@ima.UUCP (John R. Levine)
Distribution: na
Organization: Javelin Software Corporation
Lines: 13
Summary: lpt interrupt request isn't latched

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