[Coco] 9809 Halt and Catch Fire (HCF)

[Gene Heskett]

On Sunday 19 January 2020 10:48:41 Bruce W. Calkins wrote:

> An old one, although modern CPU still have it, as Gene Heskett can
> tell us.
>
> Bruce W.
>
No, if it exists, its a command I've not ever needed to use. I have heard 
of it before, but never coded it, so I can't tell any stories about it.

> On 1/18/20 10:05 PM, Melanie and John Mark Mobley wrote:
> > All,
> >
> > I did not know the 6809 had undocumented commands.  I thought the
> > undocumented commands were all NOP, BRN, LBRN.
> >
> > ---
> >
> > Source:
> > https://en.wikipedia.org/wiki/Motorola_6809
> >
> > Like the 6800, the 6809 includes an undocumented address bus test
> > instruction which came to be nicknamed Halt and Catch Fire (HCF).[1]
> >
> > References
> > [1] "Archived copy". Archived from the original on 2013-07-01.
> > Retrieved 2013-07-01.
> >
> > ---
> >
> > Archived copy:
> > https://archive.is/20130701061311/https://student.brighton.ac.uk/bur
> >ks/pcinf o/hardware/cpu.htm#selection-1145.427-1149.177
> >
> > Part VI: The 6809, extending the 680x (1977) . . . . . . . .
> > ...
> > Like the 6800, it included the undocumented HCF (Halt Catch Fire)
> > instruction to incrementally strobe the address lines for bus
> > testing ("jump to accumulator (A or B)" in the 6800, implemented and
> > documented as $00 in the 68HC11 which is described below).
> >
> > ---
> >
> > John Mark Mobley


Cheers, Gene Heskett
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