How to write procedural Verilog for this question? Vending machine should accept
ID: 3349413 • Letter: H
Question
How to write procedural Verilog for this question?
Vending machine should accept nickels (5 cents), dimes
(10 cents), and quarters (25 cents). It should dispense a product once 25 cents has been received. Vending machine must give correct change and must be a Moore-type
The finite state machine (FSM). one output per type of coin you dispense as change (e.g., if someone adds a quarter at 20 cents, you should go to a 45 cent state and output an item, and
two dimes). Maximum input 45 cents or state 9.
Explanation / Answer
module fsm_example3 (
input clk, // clock signal
input reset, // synchronous active high reset signal
input in_5c, // nickel input 5 cents
input in_10c, // dime input 10 cents
input in_25c, // Quater input 25 cents
output reg Z, // Output Z candy
output reg R_5, // Return 5 cents
output reg R_10 // Return 10 cents
);
// State Assignment
parameter INITIAL = 3'd0, // Initial state
S_5 = 3'd1, // Received 5 cents
S_10 = 3'd2, // Received 10 cents
S_15 = 3'd3, // Received 15 cents
S_20 = 3'd4, // Received 20 cents
S_25 = 3'd5, // Received 25 cents
RET_5 = 3'd6, // Candy and return 5 cents
RET_10 = 3'd7, // Candy and return 10 cents
RET_15 = 3'd8, // return 10 cents first and in next clock return candy and remaining 5 cents
RET_20 = 3'd9; // return 10 cents first and in next clock return candy and remaining 10 cents
reg [2:0] cur_state, next_state;
always @ (posedge clk or posedge reset) // current state logic
begin
if (reset)
cur_state <= INITIAL;
else
cur_state <= next_state;
end
always @(*) // next state logic and output logic
begin
next_state = cur_state;
case (cur_state)
INITIAL : begin
Z = 1'b0;
R_5 = 1'b0;
R_10 = 1'b0;
if (in_5c)
next_state = S_5;
else if (in_10c)
next_state = S_10;
else if (in_25c)
next_state = S_25;
end
S_5 : begin
Z = 1'b0;
R_5 = 1'b0;
R_10 = 1'b0;
if (in_5c)
next_state = S_10;
else if (in_10c)
next_state = S_20;
else if (in_25c)
next_state = RET_5;
end
S_10 : begin
Z = 1'b0;
R_5 = 1'b0;
R_10 = 1'b0;
if (in_5c)
next_state = S_15;
else if (in_10c)
next_state = S_20;
else if (in_25c)
next_state = RET_10;
end
S_15 : begin
Z = 1'b0;
R_5 = 1'b0;
R_10 = 1'b0;
if (in_5c)
next_state = S_20;
else if (in_10c)
next_state = S_25;
else if (in_25c)
next_state = RET_15;
end
S_20 : begin
Z = 1'b0;
R_5 = 1'b0;
R_10 = 1'b0;
if (in_5c)
next_state = S_25;
else if (in_10c)
next_state = S_35;
else if (in_25c)
next_state = RET_20;
end
S_25 : begin
Z = 1'b1;
R_5 = 1'b0;
R_10 = 1'b0;
next_state = INITIAL;
end
RET_5 : begin
Z = 1'b1;
R_5 = 1'b1;
R_10 = 1'b0;
next_state = INITIAL;
end
RET_10 : begin
Z = 1'b1;
R_5 = 1'b0;
R_10 = 1'b1;
next_state = INITIAL;
end
RET_15 : begin
Z = 1'b0; // Candy will to despense while returning 5 cents
R_5 = 1'b0;
R_10 = 1'b1;
next_state = RET_5;
end
RET_20 : begin
Z = 1'b0; // Candy will be despense while returning 10 cents
R_5 = 1'b0;
R_10 = 1'b1;
next_state = RET_10;
end
endcase
end
endmodule
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