One of the most difficult aspects of microprocessors/microcontrollers is the decode and microprogramming features. To avoid dealing with these items at this stage in the experiments, I've created a test block that has Single-Pole Double-Throw (SPDT) slide switches that enable/disable each of the functions. I've also added in a reset button, and a "STEP" button that produces a "clock" which would be generated by the system clock in a real system. In addition, I've added 4 switches that allow me to enter data directly to the main 4-bit data bus. The barrel jack provides +5V regulated input to the system.