The System Controller has four external inputs: XXX$,$ C$3$C$3\text{'}$C$3,$ SYSCLKSYSCLKSYSCLK$,$ and Reset. It has one external output: ZZZ$.$ The System Controller state is represented by Q$1$Q$\_1$Q$1$ of the JK flip$-$flop.

In this circuit, the $2-$bit counter $(74$LS$161)$ uses an active$-$low load input LDLDLD$,$ an enable input ENPENPENP, an active$-$low clear input CLRCLRCLR$,$ and the clock input SYSCLKSYSCLKSYSCLK$.$ The BBB and AAA inputs are connected to ground, and the ENTENTENT input is connected to power. The two state variable outputs are QBQAQ$\_$BQ$\_$AQB$$QA$.$ The RCORCORCO output is not used.