Motorola 6809 definition
(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
There is a simulator called usim
and an assembler
by Lennart Benschop was posted to Usenet newsgroup alt.sources on 1993-11-03.