Subject: Re: ddb key sequence
To: John F. Woods <>
From: None <>
List: current-users
Date: 11/12/1994 05:52:05
John Nemeth <> wrote:

>     If you look at any slot on an ISA machine, with the front of the
>machine facing towards you, the last pin on the right nearest the back
>of the machine is the I/O Channel Check pin.  Momentarily grounding
>this pin will produce an NMI.  Under DOS, if not redirected, the BIOS
>would report this as an Off Board Parity Error and halt the machine.
>Periscope, a company that makes DOS debuggers, sells a switch for this
>purpose, intended for forcing an entry to their debugger.  You could
>rig up something yourself.  You need a normally open pushbutton switch
>with one wire going to a good ground point and another wire going to a
>slot, stick it in the slot then stick in a card being real careful not
>to short adjacent pins.

If you're feeling ambitious, I'd think that a little r/c combo to
'de-bounce' the button would be prudent- Ordinary push-buttons generally
make too much noise to use on a logic line directly. I don't have a good
reference book nearby, so I'll leave the specifics up to someone more

'course, I have a Mac II, which came with NMI and Restart buttons built in. ;-)

Resident Quack                  NEVER INSTALL LOTS OF NEW SOFTWARE AT ONCE.
Macintosh Geek                        -Mike Landis,