[HDLBits] Fsm serialdata

See also: Serial receiver

Now that you have a finite state machine that can identify when bytes are correctly received in a serial bitstream, add a datapath that will output the correctly-received data byte. out_byte needs to be valid when done is 1, and is don't-care otherwise.

Note that the serial protocol sends the least significant bit first.

module top_module(
    input clk,
    input in,
    input reset,    // Synchronous reset
    output [7:0] out_byte,
    output done
); //
	reg [3:0] state,next;
    //0：还没接到起始位，1：接到起始位，...，9：接到最后一个数据位，10：接到终止位，11：没接到终止位
    always@(*) begin
        case(state)
            0:next<=in?0:1;
            1:next<=2;
            2:next<=3;
            3:next<=4;
            4:next<=5;
            5:next<=6;
            6:next<=7;
            7:next<=8;
            8:next<=9;
            9:next<=in?10:11;
            10:next<=in?0:1;
            //接到终止位后接到0即开始位，那就直接跳到1
            11:next<=in?0:11;
            //判断是否接到终止位。这里是设置了两种终止位状态来判断是否done
        endcase
    end

    always@(posedge clk) begin
        if(reset)
            state<=0;
        else
            state<=next;
    end
    assign done=(state==10);
    // Use FSM from Fsm_serial
    always@(posedge clk) begin
        case(state)
            1:out_byte[0]<=in;
            2:out_byte[1]<=in;
            3:out_byte[2]<=in;
            4:out_byte[3]<=in;
            5:out_byte[4]<=in;
            6:out_byte[5]<=in;
            7:out_byte[6]<=in;
            8:out_byte[7]<=in;            
        endcase
    end
    // New: Datapath to latch input bits.

endmodule