Up Down Counter

Problem Statement: Design and simulate a four-bit Up Down Counter.

What is Counter?

A counter is a sequential circuit that keeps on counting specific event. It is used in digital electronics for counting purpose.
The counter has a defined width N, which means that it can count maximum up to 2N-1 and then rolls back to 0.

Here, we will design a 4-bit Up Down counter. Based on a control signal named up_down, the counter will either count up or down from the current state of the counter.

Implementing a 4-bit up down counter

  1. Create a new Verilog file named up_down_counter.v, and copy-paste the below design of 4-bit up down counter.

  2. Create a new Verilog file and type the below testbench code provided below. Save the file with the same name as the module name.

  3. Compile the code and check for any syntax errors using the below command.

    iverilog up_down_counter.v tb_up_down_counter.v -o up_down_counter

  4. If there are no errors, use the below command for running the simulation.

    vvp up_down_counter

    You will see the values of signals being monitored across each clocktick.

  5. If all looks well, use the below command for viewing the waveform. Add the signals from tb_up_down_counter design to the window to view the simulation output as shown in below image.

    gtkwave up_down_counter.vcd