Prerequisite – Counters in Digital Logic
Problem :
Design 4 bit up-down synchronous counter Verilog Hardware Description Language along with Testbench
Design Specification :
The counter is a digital sequential circuit and here it is a 4 bit counter, which simply means it can count from 0 to 15 and vice versa based upon the direction of counting (up/down).
- The counter (“count“) value will be evaluated at every positive (rising) edge of the clock (“clk“) cycle.
- The Counter will be set to Zero when “reset” input is at logic high.
- The counter will be loaded with “data” input when the “load” signal is at logic high. Otherwise, it will count up or down.
- The counter will count up when the “up_down” signal is logic high, otherwise count down.
Verilog HDL Code :
Design –
// Here we will learn to write a verilog HDL to design a 4 bit counter module counter(clk,reset,up_down,load,data,count); //define input and output ports input clk,reset,load,up_down; input [3:0] data; output reg [3:0] count; //always block will be executed at each and every positive edge of the clock always@(posedge clk) begin if(reset) //Set Counter to Zero count <= 0; else if(load) //load the counter with data value count <= data; else if(up_down) //count up count <= count + 1; else //count down count <= count - 1; end endmodule :counter
Testbench :
// Code your testbench here module counter_tb; reg clk,reset,load,ud; reg [3:0] data; wire [3:0] count; // instance counter design counter ct_1(.ud(up_down),.*); //clock generator initial begin clk = 1'b0; repeat(30) #3 clk= ~clk;end //insert all the input signal initial begin reset=1'b1;#7 reset=1'b0; #35 reset=1'b1;end initial begin #12 load=1'b1; #5 load=1'b0;end initial begin #5 ud=1'b1;#24 ud=1'b0;end initial begin data=4'b1000;#14 data=4'b1101;#2 data=4'b1111;end //monitor all the input and output ports at times when any inputs changes its state initial begin $monitor("time=%0d,reset=%b,load=%b,ud=%b,data=%d,count=%d", $time,reset,load,ud,data,count);end endmodule :counter_tb
Expected Output :
time=0,reset=1,load=x,ud=x,data= 8,count= x time=3,reset=1,load=x,ud=x,data= 8,count= 0 time=5,reset=1,load=x,ud=1,data= 8,count= 0 time=7,reset=0,load=x,ud=1,data= 8,count= 0 time=9,reset=0,load=x,ud=1,data= 8,count= 1 time=12,reset=0,load=1,ud=1,data= 8,count= 1 time=14,reset=0,load=1,ud=1,data=13,count= 1 time=15,reset=0,load=1,ud=1,data=13,count=13 time=16,reset=0,load=1,ud=1,data=15,count=13 time=17,reset=0,load=0,ud=1,data=15,count=13 time=21,reset=0,load=0,ud=1,data=15,count=14 time=27,reset=0,load=0,ud=1,data=15,count=15 time=29,reset=0,load=0,ud=0,data=15,count=15 time=33,reset=0,load=0,ud=0,data=15,count=14 time=39,reset=0,load=0,ud=0,data=15,count=13 time=42,reset=1,load=0,ud=0,data=15,count=13 time=45,reset=1,load=0,ud=0,data=15,count= 0
Note : Follow this link to online simulate this design.
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