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'[OT] Funny mnemonics = HCF'
2000\02\01@065616 by paulb

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Russell Hedges wrote:

>         I got into this one late, but does anyone remember HCF?
>         Halt Catch Fire?  From the 6502 days of yore.

 Yes, but as I remember, it applied to the 6800/6802.  Whether it was
deliberately copied into the 6502, I don't recall.
--
 Cheers,
       Paul B.

2000\02\01@123631 by Harold M Hallikainen

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On Tue, 1 Feb 2000 22:54:25 +1100 "Paul B. Webster VK2BZC"
<spam_OUTpaulbTakeThisOuTspamMIDCOAST.COM.AU> writes:
> Russell Hedges wrote:
>
> >         I got into this one late, but does anyone remember HCF?
> >         Halt Catch Fire?  From the 6502 days of yore.
>
>   Yes, but as I remember, it applied to the 6800/6802.  Whether it
> was
> deliberately copied into the 6502, I don't recall.
> --
>   Cheers,
>         Paul B.

       I did a lot of 6800 stuff quite a while back, but don't recall HCF as an
instruction. Could it have, instead, referred to a bit of the status
register, the half-carry flag (carry from bit 3 to 4 used in the Decimal
Adjust Accumulator instruction)?

Harold


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2000\02\01@163526 by paulb

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Harold M Hallikainen wrote:

>  I did a lot of 6800 stuff quite a while back, but don't recall HCF as
> an instruction. Could it have, instead, referred to a bit of the
> status register, the half-carry flag (carry from bit 3 to 4 used in
> the Decimal Adjust Accumulator instruction)?

 Heh heh.  No.  It referred to the two undocumented instructions
corresponding to opcodes $9D and $DD which were grudgingly referred to
by Motorola as test instructions.  These switched off all processing of
opcodes until the next reset causing the processor to endlessly perform
instruction fetches.

 Rather than a SLEEP instruction, these were DIE or ZOMBIE calls,
however you chose to interpret it.  Actually, they had their uses for -
testing!

 Along with the other undocumented instructions (always a fun subject
for microprocessors) such as NBA (AND B accumulator to A) and the
various Store Immediate instructions (guess what they did?), these were
documented in the article on page 85 of Byte Magazine, January 1978.

 Remember BYTE magazine?  Used to discuss programming of computers,
algorithmic development, hardware design and such.  Those were the days!
--
 Cheers,
       Paul B.

2000\02\01@180257 by Walter Banks

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>
>         I did a lot of 6800 stuff quite a while back, but don't recall
HCF as an
> instruction. Could it have, instead, referred to a bit of the status
> register, the half-carry flag (carry from bit 3 to 4 used in the Decimal
> Adjust Accumulator instruction)?

Many years ago (late 70's) Gerry Wheeler exhaustively checked the
execution of the undocumented opcodes in the 6800/6802 for a project
we were working on. Two of the undocumented op codes ($D9 and $DD)
caused the address bus to cycle continuously through a binary count
and the instruction would never complete (HCF). Gerry wrote up the
definition of the undocumented op-codes in an article in Byte.

Walter Banks

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