[Coco] 6309 MULD real and emulators

[Robert Gault]

There was a question posted about the 6309 opcode MULD. That is a multiplication of the content of 
regD with Immediate, Direct, Extended, or Indexed numbers. What makes it different from the opcode 
MUL is that MULD is a signed multiplication.

However, be warned that while for a real 6309, and the MAME/MESS emulator MULD is signed, it is 
unsigned with VCC v2.0.1. VCC should be corrected!
ex.
  real 6309
  ldd #$8001
  muld #$8001
  regQ = $3FFF0001

  VCC
  ldd #$8001
  muld #$8001
  regQ = $40010001     Correct if the multiplication was unsigned.

You can get the same $3FFF0001 answer with
real 6309
  ldd #$7FFF
  muld #$7FFF
regQ = $3FFF0001

Now since $10000-$7FFF=$8001 the above signed math makes sense as $8001=-$7FFF.

Robert