Couldn't think of a decent example off the top of my head.
Also, proper term is 'undocumented opcodes' for further searching.
Try
"AXS * (SAX)
AXS ANDs the contents of the A and X registers (without changing the
contents of either register) and stores the result in memory.
AXS does not affect any flags in the processor status register."
Comments
I thought TAX was one of the standard 6502 opcodes?
Couldn't think of a decent example off the top of my head.
Also, proper term is 'undocumented opcodes' for further searching.
Try
"AXS * (SAX) AXS ANDs the contents of the A and X registers (without changing the contents of either register) and stores the result in memory. AXS does not affect any flags in the processor status register."
http://www.ffd2.com/fridge/docs/6502-NMOS.extra.opcodes