(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
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
<[email protected]> was posted to Usenet newsgroup alt.sources
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