Vending machine X77254

We have to design the control of a vending machine that dispenses a bag of cookies for 3€. The machine only accepts 1€ and 2€ coins. The machine has a coin slot that detects the insertion of a coin and distinguishes between 1€ and 2€ coins. Each time a coin is inserted, a 1-cycle pulse is generated on signal E1 or E2, depending on the type of coin. Since the machine only has one coin slot, no two coins can be inserted simultaneously.

After the insertion of 3€, the machine must dispense a bag of cookies by activating a signal called Cookies for one cycle. Additionally, if the customer has inserted 4€, the machine will dispense a 1€ change by activating the signal Change on the same cycle the cookies are dispensed.

The machine will not accept more coins while the cookies and the change are dispensed.

The following figure illustrates a possible waveform of the vending machine control.

Specification

module Vending_Machine(E1, E2, Cookies, Change, clk, rst);
    input E1, E2, clk, rst;
    output Cookies, Change;

Hint

The state machine can be implemented with 5 states.

Input

• E1 is the input indicating the insertion of a 1€ coin.

• E2 is the input indicating the insertion of a 2€ coin.

• clk is the clock signal.

• rst is the synchronous reset signal.

Output

• Cookies is the output that activates the delivery of cookies.

• Change is the output that activates the return of change.