6502 instructions
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Below are some references for the 6502 instruction set:
- CPU unofficial opcodes, including a full opcode matrix of all official and unofficial opcodes
- Programming with unofficial opcodes
- 6502 assembly optimisations
- Delay code, how to create a delay of a precise number of CPU cycles with smallest number of code bytes
External links
- http://obelisk.me.uk/6502/reference.html - Instruction reference with flag behavior and timing
- http://users.telenet.be/kim1-6502/6502/proman.html - MOS 6502 programming manual
- http://nesdev.org/6502_cpu.txt - Includes tick-by-tick breakdowns of instructions (see CPU interrupts for breakdowns of interrupts)
- Visual 6502 can be used to figure out obscure instruction behavior. There's also a 2A03 version available (please avoid shift-reloading it as it is hosted on a limited uplink; normal reloading should work fine and should catch any updates to the data files). There is also a tutorial on reading the circuit diagrams available, aimed at beginners.
