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Altera_Forum's avatar
Altera_Forum
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10 years ago

#in Verilog

HI, I have a question what is# 1 in the command here. Is it just a comment. Sorry, im a newbie in verilog. 

  module simple_counter (
                        CLOCK_50,
                        counter_out
                       ); 
input             CLOCK_50 ;                       
output    counter_out;
reg        counter_out;
                      
always @ (posedge CLOCK_50)          // on positive clock edge
  begin
  counter_out <=# 1 counter_out + 1;// increment counter
  end 
endmodule                           // end of module counter
module simple_counter (
                        CLOCK_50,
                        counter_out
                       ); 
input             CLOCK_50 ;                       
output    counter_out;
reg        counter_out;
                      
always @ (posedge CLOCK_50)          // on positive clock edge
  begin
  counter_out <= #1 counter_out + 1;// increment counter
  end 
endmodule                           // end of module counter

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    10 years ago

    --- Quote Start ---

    HI, I have a question what is# 1 in the command here. Is it just a comment. Sorry, im a newbie in verilog. 

      module simple_counter (
                        CLOCK_50,
                        counter_out
                       ); 
input             CLOCK_50 ;                       
output    counter_out;
reg        counter_out;
                      
always @ (posedge CLOCK_50)          // on positive clock edge
  begin
  counter_out <=# 1 counter_out + 1;// increment counter
  end 
endmodule                           // end of module counter
module simple_counter (
                        CLOCK_50,
                        counter_out
                       ); 
input             CLOCK_50 ;                       
output    counter_out;
reg        counter_out;
                      
always @ (posedge CLOCK_50)          // on positive clock edge
  begin
  counter_out <= #1 counter_out + 1;// increment counter
  end 
endmodule                           // end of module counter

    --- Quote End ---

    # 1 indicates that the output "counter_out" is delayed by 1 time unit after the rising edge of the clock. The units (ns, ps, etc.) are defined by a separate `timescale statement or the system verilog command "timeunit." At any rate, it's not shown in your code. I've come across many designers in my career who put a delay in every single line of their synthesizable code so it looks more realistic in the simulator. I do NOT recommend this, as this will affect the simulator speed. And quite frankly, it's a nuisance to type. In addition, these delays are ignored by synthesis tools, and many of them will print out a warning that the delay was ignored for every statement.

    However, delays such as these are very useful and necessary in testbenches.

    Robert

    lead VHDL/Verilog trainer

    www.digitaldesignconcepts.org (http://www.digitaldesignconcepts.org)