(Word Problem) Your task is to design the control for a news-paper vending machine to the following specification. The news-paper costs 50 cents. The vending machine accepts nickels, dimes, and quarters. The customer presses a START button and then begins entering coins. Coin sorter logic indicates to the FSM whether a nickel (N), dime (D), or quarter (Q) has been deposited. (Assume that the FSM advances from one state to the next when a coin is deposited.) If exact change is entered, a latch is released so the customer can get the paper. If the amount of money deposited exceeds 50 cents, the deposited coins are refunded to the customer by asserting a refund (REF) signal. Assume that the money just deposited is kept separated from previously accepted coins. The latter are held in a coin reposi-tory. Otherwise, the deposited coins join the repository as the FSM asserts a release (REL) signal. The block diagram for the FSM is shown in Figure Ex. 7.31.
Consider for a moment the signals that indicate the number of nickels and dimes available to make change. What is the maxi-mum number of nickels needed at any time? What is the maxi-mum number of dimes needed? Understanding the answers to these questions may help to simplify your state diagram.
Complete a Mealy machine state diagram for the vending machine control.
