[fpc-devel]Re: Latest status

Anton Tichawa anton.tichawa at chello.at
Thu Nov 29 22:30:59 CET 2001


Let me contribute a totally different version of the HCF thing .. I
programmed 8-bit microprocessors in the early 1980s, and I remember of
one -undocumented- instruction, that caused the processor (I think, 6502,
6800 or somthing like that) to increment it's address lines forever. I don't
remember if it really was CF, but if someone is interested in this I can
look for it.

We actually used this instruction, because a processor simply incrementing
it's address lines is very helpful in finding hardware errors, because
nearly every pin in the whole system then shows a certain 'signature' (that
is, low - high - transitions over all 65536 addresses). After executing this
HCF instruction, we could compare the signal on each pin with a printout of
an error-free hardware.

I don't know about a fire, but I agree that the power consumption may rise
in this mode.

I don't know either, if this instruction was really a flaw or if it was
intentionally designed for hardware testing.

Hope I could add some confusion to this myth.


----- Original Message -----
From: Alan Grimes <alangrimes at starpower.net>
To: <fpc-devel at deadlock.et.tudelft.nl>
Sent: Thursday, November 29, 2001 7:28 PM
Subject: Re: [fpc-devel]Re: Latest status

> Florian Klaempfl wrote:
> > >The worst thing about current IA64 is the carry-over of legacy
> > support. A dual instruction set chip is the most disgusting thing I've
> > ever heard of... Okay its not as bad as HCF but it's close. =P DAMN!!!
> > Sorry, but what is HCF?
> An old computer myth.
> There was once a machine with a serious hardware flaw such that entering
> a certain bad opcode, lets call it "HCF", caused the machine to go into
> a strange halt state in which the address lines coming out of the
> processor are toggled in a rapid-feedback loop. As you know, changing
> the state of a line requires an expense of energy which causes the
> release of heat. The ultra-rapid toggling of these lines would lead to
> an immense heat buildup eventually causing a fire. So HCF has the effect
> of causing the machine to Halt and Catch Fire. =P
> Google should be very helpful in giving more inf0z...
> --
> Waiting for a typical DOS application to crash is like waiting for hell
> to freeze over.
> http://users.erols.com/alangrimes/  <my website.
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