Re: 6800 hidden opcodes?

zonn@zonn.com (Zonn) wrote:

> 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.

6502s have this opcode as well - and on some 6502s it really can destroy
the CPU. (or so I've heard anyway...) It does something similar to the
6800's - toggling bus lines - so it may be that this is true for the
6800 as well.

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

-- 
Michael Searle - csubl@csv.warwick.ac.uk