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In 6502 assembly, an instruction is a single command to be executed by the processor. Instructions always include an opcode, and usually contain an operand.


In the example below, STA is the opcode, $10 is the operand, and the two combined is the instruction.

0001:85 10     STA $10      ; Stores the accumulator into memory location $10.

This example with RTS only has an opcode, but no operand. Even still, it is an instruction.

0001:4D        RTS          ; Return to calling subroutine.