Fig. 18.1.2 magnifies Fig. 18.1.1 to show how an individual flip-flop of the accumulator is connected to the ports. The IN command gates the value from the port to the accumulator, while the OUT command electrically connects the output of the accumulator to the port. Another complication not shown in these diagrams is that the various ports are connected by a multiplexor to a common internal bus that attaches to the accumulator. The port number which is the parameter of the IN or OUT instruction selects which port will connect to the accumulator via the multiplexor.