(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 accumulator s, rather than one in the 6502, and could combine them into a single 16-bit register. It also featured two index register s and two stack pointer s, which allowed for some very advanced addressing mode s. 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 mode s.
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 register s. 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 lennart@blade.stack.urc.tue.nl was posted to Usenet newsgroup alt.sources on 1993-11-03.
(1995-02-01)