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The 6809 was the last of the ‘classic’ 8-bit microprocessors, used in home and small business computers of the 1970s and early 1980s. It was backwards compatibl
by cmrdporcupine 3y ago
The 6809 was the last of the ‘classic’ 8-bit microprocessors, used in home and small business computers of the 1970s and early 1980s. It was backwards compatible with the 6800 but added more instructions.
This isn't really properly correct. The 6809 was backwards compatible with the 6800 only at the assembly source code level, not the opcode level. That is, I believe you could run your 6800 code through a 6809 assembler and probably get a valid program, but 6800 binaries would not run. The opcode encoding was different.
Also does a bit of a disservice to the 6809 to just call it a successor to the 6800, as it is in many ways the most "deluxe" of all the 8 bit processors. It wasn't just more instructions, but more/wider registers, as well.
- spogbiper 3y agoI was spoiled learning assembly code on the 6809. When I tried to move to the 8086 everything felt cumbersome and weird.
- joezydeco 3y agoI still have a Motorola 6809 TRM that has artwork right on the cover about how the 6809 was a "bridge" processor to transition you from the 6800 to the 68000. https://m.media-amazon.com/images/I/51Pu7b17-CL._SR600%2C315_PIWhiteStrip%2CBottomLeft%2C0%2C35_SCLZZZZZZZ_FMpng_BG255%2C255%2C255.jpg https://m.media-amazon.com/images/I/51Pu7b17-CL._SR600%2C315... Let's all pour one out for the D register.
- cmrdporcupine 3y agoKind of weird though, the 6809 was developed concurrent to the 68k, by an entirely different team at Motorola and its instruction set looked nothing like the 68000. The only thing they had in common was the "68" prefix and big-endian-ness. I guess there was also the ability to interface the 68k with 6800/6809 support chips on the bus, though. The 68000 was very VAX and PDP-11 inspired.