mc6809

Motorola 6809
6809
MC6809

   (MC6809) An eight-bit {microprocessor} from {Motorola, Inc.}

   The 6809 was a major advance over both its predecessor, the
   {Motorola 6800} and also over the {6502}.  The 6809 had two 8-bit
{accumulators}, rather than one in the 6502, and could
   combine them into a single 16-bit register.  It also featured
   two {index registers} and two {stack pointers}, which allowed
   for some very advanced {addressing modes}.  The 6809 was
   source compatible with the 6800, even though the 6800 had 78
   instructions and the 6809 only had around 59 (including a
   {SEX} instruction).  Some instructions were replaced by more
   general ones which the {assembler} would translate, and some
   were even replaced by {addressing modes}.

   Other features were one of the first multiplication
   instructions of the time, 16-bit arithmetic and a special fast
   {interrupt}.  But it was also highly optimised, gaining up to
   five times the speed of the 6800 series CPU.  Like the 6800,
   it included the undocumented HCF ({Halt and Catch Fire}) bus
   test instruction.

   The {Hitachi 6309} was a version with extra {registers}.  The
   6809 was used in the UK "{Dragon 32}" {personal computer} and
   was followed by the {Motorola 68000}.

   See also {SEX}.

   Usenet newsgroup: news:comp.sys.m6809.

   There is a simulator called {usim} and an {assembler} by
   Lennart Benschop <[email protected]> was posted
   to {Usenet} newsgroup {alt.sources} on 1993-11-03.

   (1995-02-01)