The objective of this project is to implement, in VHDL, a Finite State Machine, using the main clock of the Digilent Board to drive the state machine. The finite state machine will control a vending machine to dispense soda cans that are worth 50¢. Since this project will require several modules, consider using a mixed schematic/VHDL design, where you can use a schematic as the top level module, and have each sub-module defined in VHDL.
The vending machine has three inputs:
QUARTER: a signal that goes high and then low when a quarter has been deposited
CLOCK: a clock that will drive the FSM
RESET: a signal that will reset the FSM to its initial state
The vending machine has two outputs:
COUNT: a signal that goes high when a single quarter has been accepted. This signal should remain high for one clock cycle.
DISPENSE: a signal that goes high when the soda has been dispensed
Create a clock divider module to divide the master clock (at 50MHz) to a 1Hz clock. You may also need to create a switch debouncer for the QUARTER input to avoid confusing the FSM.
Create your state diagram that you will use to implement the FSM VHDL module. The vending machine behaves as follows:
- If the RESET input is asserted, the FSM will go to the initialization state (S_init) immediately. All of the outputs should be zero in this state.
- From the initialization state S_init, the FSM will unconditionally go to the wait state (S_wait)
- From the wait state S_wait, the FSM waits for the QUARTER switch to be activated.
- If QUARTER is asserted, the FSM goes to state S_Q1. In this state, the COUNT output is set to 1, indicating that a quarter has been accepted. The FSM will stay in this state until the QUARTER input is de-asserted. When this occurs, the FSM goes to state S_QW1, then unconditionally to state S_QW2 and the COUNT output is set to 0. The FSM waits for the QUARTER switch to be activated.
- If QUARTER is asserted while the FSM is in S_QW2, then the state machine goes to state S_Q2. In this state, the COUNT output is again set to 1. The FSM will stay in this state until the QUARTER input is de-asserted. When this occurs, the FSM goes to S_QW3, and then unconditionally to state S_dispense, the COUNT output is set to 0, and the DISPENSE output is set to 1.
- From state S_dispense, the FSM unconditionally goes to state S_init.
Your VHDL MUST have two process: a next-state process to determine the change of states, and a output_logic process, to determine the outputs.