Comment by Projectiboga

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.

> Although source compatible with the earlier Motorola 6800, the 6809 offered significant improvements over it and 8-bit contemporaries like the MOS Technology 6502

For those who don't know the history, the 6502 was initially the 6501, created to be a cut-down, cheaper alternative to the 6800 by many of the same engineers who designed the 6800 at Motorola. Since the idea of copyrighting an instruction set wasn't really a thing yet, the 6501 started out very, very similar to the 6800. Their goal was to basically make a clone of the 6800, except to cut costs so dramatically many changes had to be made, features cut, registers, instructions and interrupts removed. Even so, the 6501 was still pin for pin compatible with the 6800 until Motorola sued Mostek over it. The settlement was that Mostek change the pin out, so the 6501 became the 6502.

Chuck Peddle was the head technical sales person for the 6800 at Motorola and in every customer meeting where he showed early prototypes, customers loved the CPU but said the price was simply a non-starter. He got so sick of hearing it, he quit, joined Mostek, recruited some 6800 engineers and started the 6500 chip project to compete.

It also kept the HCF, Halt and Catch Fire, opcode.