apratt@iuvax.UUCP (09/27/84)
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
gino@voder.UUCP (Gino Bloch) (10/02/84)
[power down the line-eater] >> 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 I did the same to my Compaq a few weeks ago (using the IBM Tech Ref Manual as a guide, because Compaq won't supply info to mere users). Seems to work fine - and is even more necessary on the Compaq, which requires a minimum of 15 sec after power down before it will LET you power up again. Smoke reports follow as necessary. -- Gene E. Bloch (...!nsc!voder!gino)
gino@voder.UUCP (Gino Bloch) (10/06/84)
[RESET THAT BUG] > I installed a reset switch on a PC just a few days ago... ... > 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. > -- Allan Pratt > ...ihnp4!inuxc!iuvax!apratt In addition, if you arrange to store 1234h in location 40:72 before resetting, the L*O*N*G memory test is bypassed. I wrote the following (using debug): mov 40,ax ; that's 40 hex, but what does debug know? mov es,ax ; set es to paragraph 40 mov ax,1234 ; yes, that's hex es: mov 72,ax int 20 ; return to DOS saved it as a com file, and executed it from autoexec.bat. A freeby: I like a block cursor (or Bloch - see my signature), so this file includes code to do that as well: mov ch,0 ; first row of cursor mov cl,d ; last " " " mov ah,1 ; set cursor type int 10 ; video interrupt (all hex, natch). -- Gene E. Bloch (...!nsc!voder!gino)
seaburg@uiucdcs.UUCP (10/09/84)
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What does the change you mentioned actually do? Change some JMP
instruction?