[Coco] 9809 Halt and Catch Fire (HCF)

[Bruce W. Calkins]

An old one, although modern CPU still have it, as Gene Heskett can tell us.

Bruce W.


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/burks/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
>
>
>