This is an old revision of the document!
Table of Contents
The Motorola 6809
The 6809 is a binary-incompatible evolution of the previous 68xx series CPU. Often designed the “best 8-bit CPU of all times”, it prefigures some of the features that will make the 68000 a success.
Technical description
Registers: * A and B: two 8-bit accumulators, useable as the 16-bit D * X and Y: two index registers, used as memory pointers * U and S: user and system stacks * CC: condition flags register * DP: direct-page pointer
Instruction set and addressing modes
This is already covered elsewhere on the internet. Do I need to repeat everything? * http://public.logica.com/~burgins/emulator/com/m6809.html - Opcode summary with number of cycles, hex encoding of instruction, and brief description. * http://www.maddes.net/m6809pm/ - HTML version of the 6809 programming manual, more verbose, with cycle-by-cycle execution diagrams of all instructions.
Interrupts
- Reset: at system reset.
- NMI: non-maskable.
- IRQ
- FIQ: registers are not automatically saved (faster than IRQ, but needs manual save of used registers)
- SWI1, 2, and 3: software interrupts triggered by the SWI instruction.
Download
Datasheet, programming manual
