Verilog代码：

module bit4_bit1(
    input    clk_50M_i,
	input    rst_n_i,
	
	input    [3:0]data_i,
	input    data_en_i,
	
	output   data_o,
	output   data_en_o
);

reg    [3:0]data_i_tmp1;
reg    [3:0]data_i_tmp2;
reg    [3:0]data_i_valid;
reg         data_en_tmp1;
reg         data_en_tmp2;

reg    [3:0]cnt;

reg  data_o_tmp;
reg  data_en_o_tmp;
//进来的数据和使能打两拍同步一下
always@(posedge clk_50M_i or negedge rst_n_i)
	if(!rst_n_i)begin
	    data_i_tmp1    <= 4'b0;
		data_i_tmp2    <= 4'b0;
		data_en_tmp1   <= 1'b0;
		data_en_tmp2   <= 1'b0;
	end
	else  begin
	    data_i_tmp1    <= data_i;
		data_i_tmp2    <= data_i_tmp1;
		data_en_tmp1   <= data_en_i;
		data_en_tmp2   <= data_en_tmp1;
    end
always@(posedge clk_50M_i or negedge rst_n_i)
	if(!rst_n_i)
	    data_i_valid <= 4'b0;
	else if(data_en_tmp2)
	    data_i_valid <= data_i_tmp2;
	else
	    data_i_valid <= data_i_valid;
always@(posedge clk_50M_i or negedge rst_n_i)
	if(!rst_n_i)
	    cnt <= 4'b0;
	else if(data_en_tmp2 || (cnt>0&&cnt<4))
	    cnt <= cnt + 1'b1;
	else 
	    cnt <= 4'b0;
		
always@(posedge clk_50M_i or negedge rst_n_i)
	if(!rst_n_i)
	    data_o_tmp <= 1'b0;
	else if(cnt!=0)
	    data_o_tmp <= data_i_valid[4-cnt];
	else
	    data_o_tmp <= 1'b0;
always@(posedge clk_50M_i or negedge rst_n_i)
    if(!rst_n_i)
	    data_en_o_tmp <= 1'b0;
	else if(cnt!=0)
	    data_en_o_tmp <= 1'b1;
	else
	    data_en_o_tmp <= 1'b0;
	
assign  data_o = data_o_tmp;
assign  data_en_o = data_en_o_tmp;
endmodule

测试文件：

`timescale 1ns/1ns

module  bit4_bit1_tb();

parameter  clk_period = 20;

reg    clk_50M_i;
reg    rst_n_i;
reg    [3:0]data_i;
reg    data_en_i;



initial begin
        clk_50M_i = 1'b0;
        rst_n_i   = 1'b0;
	data_i = 4'b0000;
        data_en_i = 1'b0;
	
        #100
	rst_n_i = 1'b1;
	
	#200
	data_i = 4'b0001;
        data_en_i = 1'b1;
        #clk_period  data_en_i = 1'b0;

	#200
	data_i = 4'b0010;        
        data_en_i = 1'b1;
        #clk_period  data_en_i = 1'b0;

	#200
	data_i = 4'b0011;
        data_en_i = 1'b1;
        #clk_period  data_en_i = 1'b0;
 
	#200
	data_i = 4'b0100;
        data_en_i = 1'b1;
        #clk_period  data_en_i = 1'b0;

	#200
	data_i = 4'b0101;
        data_en_i = 1'b1;
        #clk_period  data_en_i = 1'b0;

	#200
	data_i = 4'b0110;
        data_en_i = 1'b1;
        #clk_period  data_en_i = 1'b0;

	#200
	data_i = 4'b0111;
         data_en_i = 1'b1;
        #clk_period  data_en_i = 1'b0;

	#200
	data_i = 4'b1000;
        data_en_i = 1'b1;
        #clk_period  data_en_i = 1'b0;
	
	#500
	data_i = 4'b0;
end

always #(clk_period/2) clk_50M_i = ~clk_50M_i;

bit4_bit1  bit4_bit1_inst(
    .clk_50M_i(clk_50M_i),
	.rst_n_i(rst_n_i),
	
	.data_i(data_i),
	.data_en_i(data_en_i),
	
	.data_o(),
    .data_en_o()
);

endmodule

仿真截图：