Re: C64 + 6809

From: MagerValp (
Date: 2008-09-17 17:05:46

>>>>> "RB" ==   <> writes:

RB> - are there 6809 experts amongst us?

I've done a little bit of 6809 asm (Vectrex, home-made dual 6809
project that was never finished), but I'm hardly an expert. If you
know 6502, it takes less than a day to learn 6809.

Daniel beat me to it, and as he said you need a 6809E, which supports
external clock circuitry and can tristate the bus.

RB> - beside the well known "because it can be done", is there another
RB> reason we benefit from a 6809 in a C64?

Do you need another reason? :)

I always thought the 6809 is ideal for writing your own operating
system, something I played around with 10+ years ago. If you want to
go really bonkers, mount two 6809Es with a little bus arbitration
logic in the socket to play with SMP. The 6809 doesn't hit the bus on
every clock cycle like the 6502 does, so letting two take turns should
work pretty well. I have no idea where my notes are, but ISTR RMW
instructions use the bus for three consecutive cycles, and can be used
to implement semaphores.

    ___          .     .  .         .       . +  .         .      o   
  _|___|_   +   .  +     .     +         .  Per Olofsson, arkadspelare
    o-o    .      .     .   o         +
     -       +            +    .

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