Re: 6800 hidden opcodes?

On Tue, 14 Apr 1998 15:43:57 -0600, Jess Askey <jess@magenta.com> wrote:

>This whole assembler topic is a bit off from the purpose of this list so
>I aplogize and
>this will be my last question...
> Did the 6800 have any hidden opcodes like the 6809 and others did? I
>have some opcodes
>for the 6800 that arent defined in Al's Hitachi Datasheet but they are
>clearly within
>code areas and not data? I searched the net but didn't find any info on
>them.
> The 6800 is quite a bit simpler and organized a bit differently in the
>areas where the
>mystery opcodes would be so I don't think they match with equivalent
>6809 opcodes.
> thanks for all the info. There are just so many knowlegeable hackers
>on this list that
>it is THE best resource for an answer. :-0

There was at least one undocumented opcode for the 6800. I can't remember the
hex value of it, but it's unofficial name was "HCF" or "Halt and Catch Fire".
Upon executing this opcode the processor began incrementing is address and data
lines at full clock speed (I believe, this is all from memory). Only reset would
get you out. Presumably this was used at the factory to test the processor. I
never heard of anyone making practical use of this instruction.

I really can't remember if there were other undocumented codes...

-Zonn

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Received on Tue Apr 14 15:19:33 1998