This is a Verilog code that implements a 2to4 Decoder module and a testbench to verify its functionality.
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Let's explain the code in detail:
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The not_gates module:
*********************************************************************************** * * * - It takes one input signal, `in`. * * - It has one output signal, `out`. * * - The output signal `out` is assigned the inverted value of the input * * signal `in` using the `~` operator. * * * *********************************************************************************** -
The nand_gate module:
******************************************************************************************************* * * * - It takes three input signals, `a`, `b`, and `c`. * * - It has one output signal, `out`. * * - The output signal `out` is assigned the inverted value of the logical * * AND operation (`&`) between the input signals `a`, `b`, and `c` using the `~` operator. * * * ******************************************************************************************************* -
The decoder_2to4 module:
******************************************************************************************************* * * * ---> It takes two input signals, `x` and `y`, and one enable signal `E`. * * ---> It has four output signals, `D0`, `D1`, `D2`, and `D3`. * * ---> The assignment of the output signals determines the behavior of the 2-to-4 decoder. * * ---> `D0` is assigned the logical AND operation between `x`, the inverted value of `y`, and `E`. * * ---> `D1` is assigned the logical AND operation between `x`, the inverted value of `y`, and `E`. * * ---> `D2` is assigned the logical AND operation between `x`, `y`, and the inverted value of `E`. * * ---> `D3` is assigned the logical AND operation between `x`, `y`, and `E`. * * * ******************************************************************************************************* -
The decoder_2to4_tb module (testbench):
************************************************************************************************************************** * * * ---> It declares three registers, `x`, `y`, and `E`, as inputs to the testbench. * * ---> It declares four wires, `D0`, `D1`, `D2`, and `D3`, as the outputs of the testbench. * * ---> It instantiates a `decoder_2to4` module instance called `dut` and connects its input and output ports * * to the signals in the testbench. * * ---> The testbench includes an `initial` block to simulate the behavior and perform the test cases. * * ---> The values of `x`, `y`, and `E` are changed in different modes to simulate different input combinations. * * ---> After each change in inputs, a delay of 10 time units (`#10`) is added, allowing the signals to propagate. * * ---> Then, the results are displayed using the `$display` function. * * ---> The displayed output values are compared to the expected values for each test case using the `!==` operator. * * If any of the test cases fail, an error message is displayed. * * ---> Finally, after all the test cases have been executed, a message is displayed indicating if all the test * * cases passed or not. * * * ************************************************************************************************************************** -
The testbench verifies the functionality of the decoder_2to4 module by testing it with eight different input modes and checking the corresponding output values. If all the test cases pass, a success message is displayed; otherwise, a failure message is displayed.
