Re: 6800 hidden opcodes?

On Tue, 14 Apr 1998 14:56:24 -0700 (PDT), aek@spies.com (Al Kossow) wrote:

>there aren't any 'hidden' opcodes, but there were other 6800
>
>familiy procesors with more instructions.

There was the 6803/6303 processors which used a superset of the 6800
instruction.

It included a MUL instruction which multiplied the A and B register and left the
results in the D register (which was the A and B registers combined).

I believe there were a few other instructions added to deal with the D register.
STAD and LDAD, maybe a shift D? TXD? TDX? I went looking for my old 6303
manual and couldn't find it. :^(

>the 'undefined' opcodes will do something on these old processors,
>I have the codes for 6502's and Z80's, but not 6800's

Z80's had *many* undefined opcodes. Including opcodes that allowed you to treat
the IX (and IY) register as two 8 bit registers, IXH and IXL. That was cool. I
never figured out why Zilog didn't just document them, near the end of the
TRS-80 era they were being used fairly regularly.

-Zonn

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Received on Tue Apr 14 15:29:43 1998