Lab #7: LatchesSAIT- ENT-DIGI-210

Lab #7: Latches

Updated May 18, 2019

Lab Description:

Construct and analyze basic Latch circuits.

Outline Objectives:

Learning outcome 9: Analyze the operating characteristics of latches and flip-flops.

Pre-Lab Preparation:

  • Complete procedure #1, part 1:
  • Design a circuit
  • Create the circuit with circuit simulation software
  • Complete procedure #2, part 1:
  • Design a circuit
  • Create the circuit in circuit simulation software

Equipment Required:

Parts kit and Vulcan Board

7400 NAND

7402 NOR

Momentary contact switch

Evaluation:

Complete the design, showing all work.

Build and analyze a circuit.

Answer the questions.

Additional Notes:

Latches and Flip Flops are a very important family of circuits used in digital electronics. As such, this and the following labs are very important exercises to gain understanding of these circuits. Please take advantage of the learning opportunity these labs provide.

Procedure 1:

Create a NAND-based Latch

1. Use circuit simulation software to design a basic latch circuit from NAND gates.

2. Wire the circuit on your breadboard. Use the LEDs on the Vulcan board.

3. Operate each switch and observe the operation of the latch. Fill in the following table. Note: The “initial state” is the output state prior to applying the indicated S and R inputs. The “mode” is the name of the input state.

4. Complete the table below. The Initial state is the state of the outputs before the input was applied. The mode is the name of the state for that row.

5. Answer the questions in procedure 3.

6. Demonstrate the function of your circuit to the instructor.

Initial / Final
S / R / Q / Q’ / Q / Q’ / Mode
1 / 1 / 0 / 1
0 / 1 / 0 / 1
1 / 0 / 0 / 1
0 / 0 / 0 / 1
1 / 1 / 1 / 0
0 / 1 / 1 / 0
1 / 0 / 1 / 0
0 / 0 / 1 / 0

Table 1-1 NAND LATCH

Procedure 2:

Create a NOR-based Latch

1. Use circuit simulation software to design a basic latch circuit from NOR gates.

2. Wire the circuit on your breadboard. Use the LEDs on the Vulcan board.

3. Operate each switch and observe the operation of the latch. Fill in the following table. Note: The “initial state” is the output state prior to applying the indicated S and R inputs. The “mode” is the name of the input state.

4. Complete the table below. The Initial state is the state of the outputs before the input was applied. The mode is the name of the state for that row.

5. Answer the questions in procedure 3.

6. Demonstrate the function of your circuit to the instructor.

Initial / Final
S / R / Q / Q’ / Q / Q’ / Mode
1 / 1 / 0 / 1
0 / 1 / 0 / 1
1 / 0 / 0 / 1
0 / 0 / 0 / 1
1 / 1 / 1 / 0
0 / 1 / 1 / 0
1 / 0 / 1 / 0
0 / 0 / 1 / 0

Table 1-2 NOR LATCH

Procedure 3:

Answer the following questions:

  1. Which of the latches is active low?______
  1. Define the term active low: ______

______

  1. Describe a procedure that can help determine if a latch has active high or active low inputs.

______

______

Signature Procedure 1 (circuit, circuit simulation, table): ______

Signature Procedure 2 (circuit, circuit simulation, table): ______

Signature Procedure 3 (questions): ______

Student Name: ______Date: ______

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