from
The Free On-line Dictionary of Computing (8 July 2008)
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)