题解 | #自动贩售机2#
自动贩售机2
https://www.nowcoder.com/practice/298dec1c3dce45c881f3e53e02558828
这种方式虽然将输入打了一拍来匹配时序，作为状态机，它没有像别的答案那样（至少明面上）引入latch，但它却莫名可以跑通。不知道是不是编译器自己引入了latch呢？
这种逻辑理解虽然不如计数器简单，但输出没有使用组合逻辑来匹配testbench的时序，也算有它的独特优势。
`timescale 1ns/1ns
module seller2(
input wire clk ,
input wire rst ,
input wire d1 ,
input wire d2 ,
input wire sel ,
output reg out1,
output reg out2,
output reg out3
);
//*************code***********//
localparam S0 = 0;
localparam S0_5 = 1;
localparam S1 = 2;
localparam S1_5 = 3;
localparam S2 = 4;
// localparam S2_5 = 4;
reg [2:0] state, nexts;
reg [2:0] dreg;
always@(posedge clk or negedge rst)
begin
if(!rst)
dreg <= 0;
else
dreg <= {sel,d2,d1};
end
always@(posedge clk or negedge rst)
begin
if(!rst)
state <= S0;
else
state <= nexts;
end
always@(*)
begin
if(!rst)
nexts = S0;
else
case(state)
S0: case(dreg[1:0])
2'b01: nexts = S0_5;
2'b10: nexts = S1;
default: nexts = state;
endcase
S0_5: case(dreg[1:0])
2'b01: nexts = S1;
2'b10: nexts = sel?S1_5:S0;
default: nexts = state;
endcase
S1: case(dreg[1:0])
2'b01: nexts = sel?S1_5:S0;
2'b10: nexts = sel?S2:S0;
default: nexts = state;
endcase
S1_5: case(dreg[1:0])
2'b01: nexts = sel?S2:S0;
2'b10: nexts = sel?S0:S0;
default: nexts = state;
endcase
S2: case(dreg[1:0])
2'b01: nexts = sel?S0:S0;
2'b10: nexts = sel?S0:S0;
default: nexts = state;
endcase
default : nexts = S0;
endcase
end
always@(posedge clk or negedge rst)
begin
if(!rst)
begin
out1 <= 0;
out2 <= 0;
out3 <= 0;
end
else if (state==S0_5)
case(dreg)
3'b010: out1 <= 1;
default: begin out1 <= 0; out2 <= 0; out3 <= 0; end
endcase
else if (state==S1)
case(dreg)
3'b001: out1 <= 1;
3'b010: begin out1 <= 1; out3 <= 1; end
default: begin out1 <= 0; out2 <= 0; out3 <= 0; end
endcase
else if (state==S1_5)
case(dreg)
3'b110: out2 <= 1;
default: begin out1 <= 0; out2 <= 0; out3 <= 0; end
endcase
else if (state==S2)
case(dreg)
3'b101: out2 <= 1;
3'b110: begin out2 <= 1; out3 <= 1; end
default: begin out1 <= 0; out2 <= 0; out3 <= 0; end
endcase
else
begin
out1 <= 0;
out2 <= 0;
out3 <= 0;
end
end
//*************code***********//
endmodule
