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From: bob@nbires.UUCP (Bob Bruck)
Newsgroups: net.micro.pc
Subject: Re: Parity Check 1  message (8253 Timer, really)
Message-ID: <438@nbires.UUCP>
Date: Wed, 17-Jul-85 11:17:29 EDT
Article-I.D.: nbires.438
Posted: Wed Jul 17 11:17:29 1985
Date-Received: Sat, 20-Jul-85 14:50:20 EDT
References: <205@geowhiz.UUCP> <185@teneron.UUCP> <2026@ut-ngp.UTEXAS>
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Organization: NBI,Inc, Boulder CO
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> ...I was playing around with the timer chip,
> trying to discover how to program it to drive the speaker, working from
> the Technical Refference Manual.
> 
> What I did was use the sequence that the BIOS uses to make the error
> beep during the start up diagnostics, but changing some of the
> parameters.  (No, I don't remember which I/O ports correspond to the
> timer chip.)  In addition to the many varied error messages and lockups
> I got as a result, one time the "PARITY ERROR 1" message appeared on
> the screen, and the soft reboot didn't work.
> 
> I would have thought that the timer chip wasn't so essential to the
> opperation of the pc.  I though the 8088 used it's own internal clock.
> Oh well, maybe someone out there can tell me how to get the timer chip
> to work the speaker.
> -- 
> 
The 8253 contains 3 clock channels.  Channel 0 is used for the software driven
time-of-day clock, channel 1 is used for memory refresh, and channel 2 is used
to support the tone generation for the audio speaker, producing a square wave
at 1.19318 MHz.  See the IBM PC technical reference for more details.

Given this, you probably accidentally  re-programmed channel 1, disabling
memory refresh and thus causing the parity error you described.

					Bob Bruck
					(hao | allegra | ...)!nbires!bob