(Word Problem) You are to design the state diagram for a simple controller that turns a lamp on and off at preset times. This is a timed light switch. The finite state machine has six inputs: Reset, Set Time, SetLiteOn, SetLiteOff, Run, and Advance. The first five inputs are generated by a five-position rotary switch that advances through Reset, Set Time, SetLiteOn, SetLiteOff, and Run (the inputs are mutually exclusive and are encountered in the specified order). The Advance input is a push-button. See Figure Ex. 10.6(a). When you hold the Advance button down (asserted), the displayed time rapidly advances through 24 hours, a minute at a time.
The typical operation of the timed light switch works as follows. It is normally in Run mode. The lamp is turned on when-ever the internal clock matches an internal register (LiteOn) that holds the time to turn the light on. The lamp is turned off whenever the internal clock matches an internal register fLiteOffl that holds the time to turn the light off.
To operate the timed light switch, you must set the current time, then the time on, and finally the time off. This is accomplished as follows. The mode switch is moved from Run to Reset. This causes an internal timer register to be loaded with the time 08:00. Next, the mode switch is moved to the SetTime position. When-ever Advance is pushed and held down, the timer register rapidly cycles through the minutes and hours. You "pulse" or single step
Advance as it gets close to the current time. When you move the switch to SetLiteOn, the current value in the timer register over-writes the value in the internal clock register. At the same time, the internal timer register is reset to 08:00. By working with the Advance button, you set a new time at which the light is to be turned on. Moving the mode switch to SetLiteOff causes the LiteOn register to be overwritten by the timer register.
Using the Advance button once again, you advance the timer from its last value (the "lights on" time) to the desired time to turn the lights off. Once the mode switch is set to Run, the timed light switch goes into its running mode. The data path associated with the timed light switch is shown in Figure Ex. 10.6(b). The block diagram is given in Figure Ex. 10.6(c). Complete a Moore state diagram for the timed light-switch controller.
