Design a traffic light controller at the intersection of a a heavily traveled highway and a local road. The controller is described by the following specification.
(a) The signal lights at the highway are labeled {RYG}, for Red, Yellow, and Green.
(b) The signal lights at the road are similarly labeled {r y g}, designating the respective colors.
(c) A sensor V is placed at the intersection which senses the presence (V=1) or absence (V=0) of a vehicle on the road.
(d) Initial State: Initially a G/r signal combination is applied (green on highway / red on the road).
(e) Normal Mode: If there are no vehicles on the road, the G/r signal combination is maintained.
(f) Emergency Mode: If a vehicle is sensed on the road, the lights should cycle from G/r to Y/r to R/g to allow the vehicle to cross the intersection. Each transition takes 5 seconds.
(g) The state R/g is maintained as long as vehicles are present at the road.
Draw a block diagram, clearly indicating the combinational portion of the design, the D flipflops, all interconnections, and all inputs and outputs.