gareth evans  wrote:
> On 22/01/2021 13:34, The Natural Philosopher wrote:
> > On 22/01/2021 13:22, gareth evans wrote:
[snip]
>
> ISTR that FORTH on an RCA 1802 is in the Voyager missions?
>
> Now, that was a weird instruction set! ISTR 8-off 16 bit
> registers but no 16-bit moves, all having to be done in
> 8-bit chunks through the accumulator, and no conventional
> subroutine call but change which of the 16-bit registers
> at any time was the program counter!
>
I worked on 1802 based systems from 1980 to 1987 in Oman.  It was all
done in assembler, I actually wrote an 1802 macro assember using the
very basic assembler that came with the RCA 1802 developement systems.

As you say it was a very odd instruction set.  You could use any one
of the 16 bit registers as the program counter which could lead to
some very confusing (and difficult to debug) code.

--
Chris Green
·

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