(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: comp.sys.m6809.
There is a simulator called usim and an assembler by
Lennart Benschop <lennart@blade.stack.urc.tue.nl> was posted
to Usenet newsgroup alt.sources on 1993-11-03.
