Motorola 6809
Motorola 6809
The 6809 was a major advance over both its predecessor, theMotorola 6800 and also over the 6502. The 6809 had two 8-bit accumulators, rather than one in the 6502, and couldcombine them into a single 16-bit register. It also featuredtwo index registers and two stack pointers, which allowedfor some very advanced addressing modes. The 6809 wassource compatible with the 6800, even though the 6800 had 78instructions and the 6809 only had around 59 (including aSEX instruction). Some instructions were replaced by moregeneral ones which the assembler would translate, and somewere even replaced by addressing modes.
Other features were one of the first multiplicationinstructions of the time, 16-bit arithmetic and a special fastinterrupt. But it was also highly optimised, gaining up tofive times the speed of the 6800 series CPU. Like the 6800,it included the undocumented HCF (Halt and Catch Fire) bustest instruction.
The Hitachi 6309 was a version with extra registers. The6809 was used in the UK "Dragon 32" personal computer andwas followed by the Motorola 68000.
See also SEX.
Usenet newsgroup: news:comp.sys.m6809.
There is a simulator called usim and an assembler byLennart Benschop