Re: GLOAT BLOAT (Was: Boot messages, Ideas for v2.1)

Kevin Lentin (kevinl@cs.monash.edu.au)
Tue, 25 Jun 1996 14:39:18 +1000 (EST)

Fred Love Wrote ...
>
> >
> > Not a UNIX, but a CPU with a similar thing. One of the first versions
> > of a CPU, I think it was the Z80, had a debugging instruction left in
> > the instruction set that would toggle the voltage levels on one pin
> > as fast as possible. This turned out to be let lethal to the electronics
> > and so the instruction was named "Halt and catch fire".
> >
> > Can't even remember where I got this story from or if it's a urban legend
> > of the computer bussines, so just take it for your personal amusement,
> >
> > Ralf
>
> No debug instructions in the Z80 instruction set, only one output
> instruction was left undocumented by Mostek.

I should have replied to Ralf but I've lost the original mail. So I'll
reply to Fred instead...

This is the HCF entry in the Jargon File:

:HCF: /H-C-F/ n. Mnemonic for `Halt and Catch Fire', any of
several undocumented and semi-mythical machine instructions with
destructive side-effects, supposedly included for test purposes on
several well-known architectures going as far back as the IBM 360.
The MC6800 microprocessor was the first for which an HCF opcode
became widely known. This instruction caused the processor to
{toggle} a subset of the bus lines as rapidly as it could; in
some configurations this could actually cause lines to burn
up.

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