instruction code Nop The instruction code 'Nop' is an instruction code of the transsmt instruction set that does nothing or modifies the behavior of the instruction code preceeding it by changing the virtual CPU component that it affects (stack or head), or acts as part of a template to denote positions in a digital organism's genome. Note that most operations that use 2 'Nop' instruction codes to specify which stacks to use can also be parameterized by a single 'Nop' instruction code, in which case the second modifier is assigned the next stack in sequence (e.g., C->D, D->A, etc.).