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.
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.
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.
There was even a multi-tasking, multi-user operating system called OS-9 created for the 6809 that was quite UNIX-like. Businesses actually connected serial terminals and supported four or more simultaneous users doing work all day on these little 8-bit, 64K micros. It was extremely capable and even quite elegant in it's architecture.
Unfortunately, in the 70s Motorola misjudged how large the market for personal microcomputers would grow and over-priced the original 6800 (1975: basic 8-bit) and 6809 (1978: advanced 8/16 bit). Even though the 6809 was more than double the clock for clock performance of a 6502 or Z80, at four times the price, it was a tough sell to consumer computer makers. By the time Motorola lowered the price, it was too late as platform choices had been made and the 68000, the 6809's 16/32-bit big brother, was just around the corner. A key reason Jobs may have been able to cut a killer deal to put the 68000 in the Mac was simply that Motorola had been losing almost every big CPU design win based on their earlier mis-estimates of the market.
But if you made a bar bet today to do something challenging on a 1970s 8-bit CPU, you'd win by picking a 6809 or, even better, its lesser-known CMOS version the 6309, created as a second-source part by Hitachi. Being CMOS the 6309 was operationally identical to the 6809 but could run at 3.5 Mhz vs the 6809's 2 Mhz. The 6309 also has a 'secret' alternate mode that saves cycles over the 6809 on many common operations as well as adding several new instructions including a hardware divide. The paper being in Japanese, I was surprised they didn't use a 6309 since it can easily be swapped into any 6809 socket for a quick boost .
Little known history: Apple's original prototypes for the Macintosh were actually based on the 6809 before Jobs negotiated his legendary discount deal for 68000 CPUs. Most pinball machines of the 80s, 90s and even early 00s were based on the 6809. I have a Simpson's Pinball Party machine released in 2003 based on a 6809. Quite a long life for not only an 8-bit ISA, but in the same 1970s package, voltage and clock speed. Interesting to see such an ancient CPU as the brain of a $3,000 modern design driving a 144-pin surface mount FPGA next to it (which probably has orders of magnitude more gates)!
I honestly was hoping for some tabletop eurogames or smth...
...reached a playing strength on par with GNU Go
What Motorola did in 1978 was to publish some articles in the specialized magazines, announcing MC6809 as the future better replacement for their existing MC6800 derivatives. This is the same like Intel describing during last year how great will be their Panther Lake CPU, but Panther Lake has really been launched only a couple of days ago.
