Day-15

Verilog explanation

Certainly, here's a full explanation of the SR latch Verilog code:

Module Declaration and Ports: The Verilog code defines a module named SR_Latch, which represents an SR latch. An SR latch is a basic digital logic element with two inputs and two outputs. The module has the following ports:

• S (Set input): This input allows you to set the latch to a specific state.
• R (Reset input): This input allows you to reset the latch to a specific state.
• Q (Q output): This output represents one of the stable states of the latch.
• Qn (Q' or not-Q output): This output represents the complementary state to Q, which is the other stable state.

Output Registers: Inside the module, two registers, Q and Qn, are declared. These registers store the current state of the outputs Q and Qn of the SR latch. The values of Q and Qn will be updated based on the SR latch's logic.

SR Latch Logic: The core functionality of the SR latch is implemented in the following always block. This block is sensitive to changes in the S and R inputs and updates the Q and Qn outputs accordingly.

• If the R input is asserted (high) and the S input is not asserted (low), the SR latch is in the reset state. In this case, the Q output becomes 0, and the Qn output becomes 1.

• If the S input is asserted (high) and the R input is not asserted (low), the SR latch is in the set state. In this case, the Q output becomes 1, and the Qn output becomes 0.

• When both S and R are either both high or both low, there is no change in state. This condition is handled by the final else block. It ensures that the SR latch maintains its current state when both inputs are simultaneously active (high) or inactive (low).

End of Module: The module definition for SR_Latch is concluded with the endmodule statement.

In summary, the provided Verilog code defines an SR latch module, which is a fundamental digital logic element. It has set and reset inputs (S and R) and two outputs (Q and Qn) representing its two stable states. The module's behavior follows the principles of an SR latch, allowing it to be instantiated and used in digital designs for tasks such as memory storage and sequential logic control.

Testbench code explanation

1. Module Declaration (SR_Latch_Testbench):

• The code starts by defining a new Verilog module named SR_Latch_Testbench. This module will serve as the testbench for the SR latch.

2. Signal Declarations:

• Inside the SR_Latch_Testbench module, we declare several signals:
  • reg S, R: These are registers used to represent the inputs of the SR latch. S represents the Set input, and R represents the Reset input.
  • wire Q, Qn: These are wires used to represent the outputs of the SR latch. Q represents the Q output, and Qn represents the Q' (complement of Q) output.

3. SR Latch Instantiation:

• The SR latch module (SR_Latch) is instantiated within the testbench using the SR_Latch_inst instance.
• The inputs and outputs of the SR latch module are connected to the corresponding signals declared earlier in the testbench.

4. Stimulus Generation (initial block):

• The initial block contains the stimulus generation part of the testbench. It is where we apply input values to the SR latch and observe the output responses.
• Here's a breakdown of the stimulus generation:
  • Inputs (S and R) are initially set to 0, representing an inactive state for both Set and Reset.
  • Test cases are applied by changing the values of S and R at specific time intervals (#10 time units).
  • For example, setting S to 1 simulates setting the latch, and setting R to 1 simulates resetting the latch.
  • After each input change, a delay is added to allow time for the SR latch to respond.
  • Additional test cases can be added as needed.
  • The simulation ends with $finish.

5. Displaying Results (always block):

• The always block is used to display the values of S, R, Q, and Qn whenever there's a rising edge on either S or R. This helps in observing the behavior of the SR latch during simulation.

6. End of Module:

• The module definition for SR_Latch_Testbench is closed.

In summary, this Verilog code creates a testbench for an SR latch module. It initializes the inputs, applies test cases, and displays the results of the SR latch's behavior during simulation. This testbench is a valuable tool for verifying that the SR latch functions as expected under various input conditions and helps ensure its correctness before incorporating it into a larger digital design.