alt Hacker NewsIt was a hybrid processor, 16 on the inside 8 bit on the bus. From Wikipedia.
The Motorola 6809 ("sixty-eight-oh-nine") is an 8-bit microprocessor with some 16-bit features. It was designed by Motorola's Terry Ritter and Joel Boney and introduced in 1978. Although source compatible with the earlier Motorola 6800, the 6809 offered significant improvements over it and 8-bit contemporaries like the MOS Technology 6502, including a hardware multiplication instruction, 16-bit arithmetic, system and user stack registers allowing re-entrant code, improved interrupts, position-independent code, and an orthogonal instruction set architecture with a comprehensive set of addressing modes.
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Mountain_Skies • yesterday at 8:07 PM
It also kept the HCF, Halt and Catch Fire, opcode.
Motorola 6809 was a great improvement over Zilog Z80 (previously the best "8-bit" processor), but unfortunately it was introduced too late, in 1979, when the transition towards 16-bit CPUs able to address more than 64 kB of memory had already started.
Motorola had made the mistake of introducing at the same time 2 different incompatible ISAs, one for CPUs covering the low-end of the market, MC6809, and one for CPUs covering the high-end of the market, MC68000. This mistake has cost them the chance of being selected for the IBM PC (because MC68000 was considered too expensive, while MC6809 was not future-proof, with its limited addressing space). After they have seen the success of Intel with its 2 software-compatible CPUs, 8086 for the high end and 8088 for the low end, Motorola has also introduced MC68008, a MC68000 variant for cheaper computers, but it was too late, as the IBM PC became dominant.