写了好多遍，终于对了。关键点在于：
1. 输入都为0时，小于1.5元的状态的nxt_state应该保持不变，因为在下降沿时输入会变化，所以不能让nxt_state=cur_state；
2. cur_state大于等于1.5元时应该继续检测输入，否则钱丢进入就没了（某个解答直接将nxt_state都置为ZERO）;
小技巧：
用case(1'b1)和d1/d2/d3匹配会省面积。
`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***********//
    localparam ZERO=3'b000,HALF=3'b001,ONE=3'b011,ONEHALF=3'b010;
    localparam TWO=3'b110, TWOHALF=3'b111, THREE=3'b101;
    
    reg [2:0] cur_state,nxt_state;
    always @(posedge clk, negedge rst) begin
        if (rst==0)
            cur_state <= ZERO;
        else
            cur_state <= nxt_state;
    end
    
    always @(*) begin
        case(cur_state)
            ZERO: 
                case(1'b1)
                    d1: nxt_state = HALF;
                    d2: nxt_state = ONE;
                    d3: nxt_state = TWO;
                    default: nxt_state = nxt_state;
                endcase
            HALF: 
                case(1'b1)
                    d1: nxt_state = ONE;
                    d2: nxt_state = ONEHALF;
                    d3: nxt_state = TWOHALF;
                    default: nxt_state = nxt_state;
                endcase
            ONE: 
                case(1'b1)
                    d1: nxt_state = ONEHALF;
                    d2: nxt_state = TWO;
                    d3: nxt_state = THREE;
                    default: nxt_state = nxt_state;
                endcase
            ONEHALF: 
                case(1'b1)
                    d1: nxt_state = HALF;
                    d2: nxt_state = ONE;
                    d3: nxt_state = TWO;
                    default: nxt_state = ZERO;
                endcase
            TWO: 
                case(1'b1)
                    d1: nxt_state = HALF;
                    d2: nxt_state = ONE;
                    d3: nxt_state = TWO;
                    default: nxt_state = ZERO;
                endcase
            TWOHALF: 
                case(1'b1)
                    d1: nxt_state = HALF;
                    d2: nxt_state = ONE;
                    d3: nxt_state = TWO;
                    default: nxt_state = ZERO;
                endcase
            THREE: 
                case(1'b1)
                    d1: nxt_state = HALF;
                    d2: nxt_state = ONE;
                    d3: nxt_state = TWO;
                    default: nxt_state = ZERO;
                endcase
            default: 
                case(1'b1)
                    d1: nxt_state = HALF;
                    d2: nxt_state = ONE;
                    d3: nxt_state = TWO;
                    default: nxt_state = ZERO;
                endcase
        endcase
    end
    
    always @(*) begin
        case (cur_state)
            ONEHALF: begin out1 = 1'b1; out2 = 2'd0; end
            TWO: begin out1 = 1'b1; out2 = 2'd1; end
            TWOHALF: begin out1 = 1'b1; out2 = 2'd2; end
            THREE: begin out1 = 1'b1; out2 = 2'd3; end
            default: begin out1 = 1'b0; out2 = 2'd0; end
        endcase
    end
                                                                           
//*************code***********//
endmodule
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