Motorola 6809
(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.
