6502 instructions

Below are some references for the 6502 instruction set:

• Instruction reference, describing all official instructions and how they function
• CPU unofficial opcodes, including a full opcode matrix of all official and unofficial opcodes
• Programming with unofficial opcodes
• 6502 assembly optimisations
• Delay code, and Fixed cycle delay: how to create a delay of a precise number of CPU cycles with smallest number of code bytes
• 6502 cycle times

External links

• 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)
• https://www.nesdev.org/obelisk-6502-guide/reference.html - Historical 6502 instruction reference, but largely obsoleted by NESdev's instruction reference
• Visual 6502 can be used to figure out obscure instruction behavior. There's also a 2A03 version available (hosted on residential broadband, so avoid needless shift-reloading). There is also a tutorial on reading the circuit diagrams available, aimed at beginners.