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From: apratt@iuvax.UUCP
Newsgroups: net.micro.pc
Subject: Re: Re: IBM-PC Hardware RESET kluge -> R
Message-ID: <1500021@iuvax.UUCP>
Date: Thu, 27-Sep-84 15:45:00 EDT
Article-I.D.: iuvax.1500021
Posted: Thu Sep 27 15:45:00 1984
Date-Received: Sat, 29-Sep-84 10:27:24 EDT
References: <171@alberta.UUCP>
Lines: 35
Nf-ID: #R:alberta:-17100:iuvax:1500021:000:1555
Nf-From: iuvax!apratt    Sep 27 14:45:00 1984


I installed a reset switch on a PC just a few days ago...
I determined a couple of ways of doing it, and the one I
chose is probably the worst.

	a) You could rig a button which forces a parity error,
	   and revector NMI to the keyboard-reset routine.
	   I wanted to do this, but couldn't find the place to
	   force the parity error. NMI is active-high, and when
	   the circuitry is holding the line at ground, it's
	   hard to bring it up to +5 to activate it.

	b) You could inform the computer that its power is bad.
	   that's what I did, and it works fine. The result is
	   just like cycling power, except you don't have to turn
	   off the power supply. This is especially good if you
	   have a hard disk and don't want to cycle its power.

There is a pin coming from the power supply which indicates
"power good". If you ground this signal, the entire computer is
placed in a RESET state, and, when this signal goes active again,
a complete power-up restart is executed. The power-good pin is the
one closest to the back of the computer on the motherboard. You can
ground it by connecting it (through a normally-open switch) to the
fifth or sixth pin of the power supply connection (counting from the
back to the front). I'm not exactly sure if this hurts the power
supply -- it could. Also, check those pin numbers -- I may remember
them wrong. But the thing works, and you don't have to cycle power
on the mother board, disk drives, or anything.


----
		"Fritz! They've killed Fritz!"
						-- Allan Pratt
					...ihnp4!inuxc!iuvax!apratt