Provide the finite-state machine with a diagram, description and interface signa

Question

Provide the finite-state machine with a diagram, description and interface signals, and any necessary circuit diagrams with explanations.

Consider a controller for traffic at the intersection of a 4 way junction:

The following must be considered:

1. There are 4 traffic lights ? one for each direction. Each direction has a left turn and a pedestrian crossing.

2. The priority is given to the vehicles going straight (NSG and EWG stay ?1? for the longest period).

3. These are the possible traffic lights:

NSG, NSY, NSR, NSLG, NSLY, NSLR, EWG, EWY, EWR, EWLG, EWLY, EWLR.

Where G, Y, and R refer to Green, Yellow, and Red lights.

Apart from these, traffic lights are provided for pedestrians at each stop sign (PWEW and PWNS).

4. Use counters to provide delays on transitions from states.

For instance, the NS and EW remain green for 15s, yellow for 5s, red for the rest of the time that the left turn is green. The NSL and EWL remain green for 10s and yellow for 5s. Use Fig. 2 as reference.

5. The lights for the pedestrian crossing along the EW direction (PWEW) will be green if (PBEW=1 & EWR=1 & EWLR=1 & NSLR=1). This implies that the PWEW will be green between 1 and 20 seconds. The timing diagram below illustrates:

Similarly the lights for the pedestrian crossing along the NS direction (PWNS) will be green if (PBNS=1 & NSR=1 & NSLR=1 & EWLR=1). Here, the PWNS will be green between 35 seconds and 55 seconds.

Explanation / Answer

A finite-state machine (FSM) or finite-state automaton (plural: automata), or simply a state machine, is a mathematical model of computation used to design both computer programs and sequential logic circuits. It is conceived as an abstract machine that can be in one of a finite number of states. The machine is in only one state at a time; the state it is in at any given time is called the current state. It can change from one state to another when initiated by a triggering event or condition, this is called a transition. A particular FSM is defined by a list of its states, and the triggering condition for each transition. The behavior of state machines can be observed in many devices in modern society which perform a predetermined sequence of actions depending on a sequence of events they are presented with. Simple examples are vending machines which dispense products when the proper combination of coins are deposited, elevators which drop riders off at upper floors before going down, traffic lights which change sequence when cars are waiting, and combination locks which require the input of combination numbers in the proper order. Finite-state machines can model a large number of problems, among which are electronic design automation, communication protocol design, language parsing and other engineering applications. In biology and artificial intelligence research, state machines or hierarchies of state machines have been used to describe neurological systems and in linguistics—to describe the grammars of natural languages. Considered as an abstract model of computation, the finite state machine is weak; it has less computational power than some other models of computation such as the Turing machine. That is, there are tasks which no FSM can do but a Turing machine can do. This is because the FSM has limited memory. The memory is limited by the number of states. FSMs are studied in the more general field of automata theory.

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