题解 | #自动贩售机1#
自动贩售机1
https://www.nowcoder.com/practice/dcf59e6c51f6489093495acb1bc34dd8
看了网友的讨论，输入信号只有半个时钟周期有效，另外半个时钟周期无效，nstate不能跟随输入信号变化，需要维持不变。所以不能写成：IDEL: nstate = d1?S0:(d2?S1:(d3?S3:IDEL));，而应该写成：IDEL: nstate = d1?S0:(d2?S1:(d3?S3:nstate));
`timescale 1ns/1ns module seller1( input wire clk , input wire rst , input wire d1 , input wire d2 , input wire d3 , output reg out1, output reg [1:0]out2 ); //*************code***********// moore parameter IDEL=0, S0=1, S1=2, S2=3, S3=4, S4=5, S5=6; reg [2:0] cstate, nstate; always@(posedge clk or negedge rst) begin if(!rst) begin cstate <= IDEL; end else begin cstate <= nstate; end end always@(*) begin case(cstate) IDEL: nstate = d1?S0:(d2?S1:(d3?S3:nstate)); S0: nstate = d1?S1:(d2?S2:(d3?S4:nstate)); S1: nstate = d1?S2:(d2?S3:(d3?S5:nstate)); S2, S3, S4, S5: nstate = d1?S0:(d2?S1:(d3?S3:IDEL)); default:nstate = IDEL; endcase end always@(posedge clk or negedge rst) begin if(!rst) begin out1 <= 1'b0; out2 <= 2'd0; end else begin case(nstate) S2: begin out1 <= 1'b1; out2 <= 2'd0; end S3: begin out1 <= 1'b1; out2 <= 2'd1; end S4: begin out1 <= 1'b1; out2 <= 2'd2; end S5: begin out1 <= 1'b1; out2 <= 2'd3; end default: begin out1 <= 1'b0; out2 <= 2'd0; end endcase end end //*************code***********// endmodule
