Re: 6800 hidden opcodes?

On Tue, 14 Apr 1998 15:35:22 -0700, Clay Cowgill <ClayC@diamondmm.com> wrote:

>> 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).
>>
>That's how the 6809 works too, BTW...
>
>> 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. :^(
>>
>In 6809-land those were ldd and std...

Yeah, in the 6800 world they were pretty obsessed with "STA" meaning "Store
Accumulator" not "Store A-reg". So the "official" opcodes were:

 STA A
 STA B
 STA D (for the 6803 -- if this opcode really exists)

You were allowed to leave off the space and simply write:

 STAA
 STAB
 STAD

A believe you were allowed to carry that syntax over to the 6809 assemblers if
you wanted, but to make things simple they allowed things to be shortened.
Though I believe the 6809 always used the short versions for the 16 bit
registers:

 STX
 LDX
 STD
 LDD

They also allowed you not to type a zero offset from an index which I always
thought looked kinda funny:

 LDA ,X

instead of:

 LDA 0,X

I started my career (*many* moons ago) programming motor control logic in 6800
assembly language then graduated to writing assembly language device drivers for
OS-9 (A 6809 based unix type operating system that was pretty darn cool!)

I still think Motorola did the best job of designing instruction sets. Too bad
their sales/service departments have always been the worst of all
micro-processor manufacturers (with the possible exception of Texas Instruments)
or the IBM-PC just might have had a 68000 in it instead of a 8088 (which was
more like an 8080++).

-Zonn

<><><><><><><><><><><><><><><><><><><><><><><><><><><><

 ------ ___ Member of A.A.C.S.:
 |---- | ( ) Association for Artistically
    / / ( () ) Challenged Signatures
   / / //\\ // (__)
  / ---/ // \\ //\\ // zonn @ zonn . com
 -------| // \\/
Received on Tue Apr 14 16:24:34 1998