In general most instructions on the 6500 series take as many cycles as there are memory accesses, with a lower limit of two. This means no instruction will execute in less than two cycles (*1). The mentioned ADC gives a nice example, as it offers almost all addressing modes: Mode Example Length | Cycles ...


Assuming you’re asking: what can the 6502 be seen to be doing by an external observer, then the data sheet has a full breakdown of bus activity per cycle per addressing mode; that was long ago transcribed into ASCII form by the Commodore community and is now often sourced from that 64doc.txt. Do a search in that document for “Instructions accessing the stack”...


The length of the ADC Immediate is 2. One for the opcode $69 and one for the immediate. At the very least, this requires two bus cycles to fetch. On a "simple" processor, an instruction can't take fewer cycles than the number of bus cycles that need to be performed to do the work of that instruction.

Only top voted, non community-wiki answers of a minimum length are eligible