测试在不同的地方对同一信号赋值。

`timescale 10ns/1ns   module verilogtest_sim(); reg clk; reg [1:0]a, b; reg sel; reg reset; reg [1:0]out;   initial begin   clk = 0;   forever   #1 clk = ~clk; end   reg op_and, op_or;   initial begin   a = 2'b11;   b = 2'b01;   op_and = 0;   op_or = 0;   sel = 1;   reset = 1;   #4 reset = 0;   #2 reset = 1;   #5 reset = 0;   #2 reset = 1;   #8 $stop; end       always @(posedge clk) begin   if(!reset)     out <= 2'b0;   else     out <= 2'bz; end   always @(posedge clk) begin   if(!reset)     begin       op_and <= 0;       op_or <= 0;     end  else  begin   if(sel)   begin     op_and <= 1;     op_or <= 0;   end   else   begin     op_and <= 0;     op_or <= 1;   end   end end   always @(posedge clk) begin   if(op_and)     out <= a & b;   else     out <= 2'bz; end   always @(posedge clk) begin   if(op_or)     out <= a | b;   else     out <= 2'bz; end   endmodule

 

 

另一例子：

module exe(dir, a, b, out); input a, b; input [1:0] dir; output out; reg out;       always @(dir or a) begin        if(dir == 2'b01)               out <= a;        else               out <= 1'bz;   end   always @(dir or b) begin        if(dir == 2'b10)               out <= b;        else               out <= 1'bz; end   endmodule

module exe(dir, a, b, out); input a, b; input [1:0] dir; output out; reg out;       always @(dir or a or b) begin        if(dir == 2'b01)               out <= a;        else if(dir == 2'b10)               out <= b;        else               out <= 1'bz;   end     endmodule

左边的ＲＴＬ：

 

 

 

 

右边的ＲＴＬ：

 

 

 

结论：可以在不同always中对同一信号赋值，但要小心，不推荐这么做。