Introduction to the 74LS76

The 74LS76 is a member of the 74LS series of TTL (Transistor-Transistor Logic) ICs, known for their low power consumption and improved speed compared to the original 7400 series. This IC contains two independent J-K flip-flops, each with its own preset (PR) and clear (CLR) inputs, allowing for asynchronous control of the flip-flop state.

Key Features of the 74LS76

• Dual J-K flip-flops in a single package
• Asynchronous preset and clear inputs for each flip-flop
• TTL-compatible inputs and outputs
• Low power consumption
• High-speed operation
• Wide operating voltage range (4.75V to 5.25V)

74ls76 Pinout Configuration

To effectively use the 74LS76 in your circuits, it is essential to understand its pinout configuration. The 74LS76 is available in a 16-pin DIP (Dual Inline Package) format, with each pin serving a specific function. Let’s take a closer look at the pinout diagram and the role of each pin.

74LS76 Pinout Diagram

         +---+--+---+
    CLR1 |1  +--+ 16| VCC
     PR1 |2       15| CLR2
      J1 |3       14| PR2
     /Q1 |4       13| J2
     Q1  |5 74LS76 12| /Q2
     CLK1|6       11| Q2
     GND |7       10| CLK2
     Q2  |8        9| K2
         +----------+

Pin Description

1. CLR1 (Clear 1): Active-low asynchronous clear input for flip-flop 1
2. PR1 (Preset 1): Active-low asynchronous preset input for flip-flop 1
3. J1: Synchronous input J for flip-flop 1
4. /Q1: Inverted output of flip-flop 1
5. Q1: Non-inverted output of flip-flop 1
6. CLK1 (Clock 1): Clock input for flip-flop 1
7. GND (Ground): Common ground connection
8. Q2: Non-inverted output of flip-flop 2
9. K2: Synchronous input K for flip-flop 2
10. CLK2 (Clock 2): Clock input for flip-flop 2
11. Q2: Non-inverted output of flip-flop 2
12. /Q2: Inverted output of flip-flop 2
13. J2: Synchronous input J for flip-flop 2
14. PR2 (Preset 2): Active-low asynchronous preset input for flip-flop 2
15. CLR2 (Clear 2): Active-low asynchronous clear input for flip-flop 2
16. VCC (Power Supply): Positive supply voltage (usually 5V)

Functional Description

The 74LS76 contains two independent J-K flip-flops, each with its own inputs and outputs. The behavior of each flip-flop is determined by the states of its J, K, PR, and CLR inputs, as well as the clock signal. Let’s explore the various operating modes of the 74LS76.

J-K Flip-Flop Operation

The J-K flip-flop has two synchronous inputs, J and K, which control the state of the flip-flop on the rising edge of the clock signal. The flip-flop’s behavior based on the J and K inputs is summarized in the following truth table:

• When J=0 and K=0, the flip-flop maintains its current state (Q(n)) on the next clock edge.
• When J=0 and K=1, the flip-flop resets to 0 on the next clock edge.
• When J=1 and K=0, the flip-flop sets to 1 on the next clock edge.
• When J=1 and K=1, the flip-flop toggles its state (Q(n+1) = /Q(n)) on the next clock edge.

Asynchronous Preset and Clear

In addition to the synchronous J and K inputs, each flip-flop in the 74LS76 has asynchronous preset (PR) and clear (CLR) inputs. These inputs allow you to set or reset the flip-flop independently of the clock signal.

• When PR is low (logic 0), the flip-flop is immediately set to 1, regardless of the clock state or the J and K inputs.
• When CLR is low (logic 0), the flip-flop is immediately reset to 0, regardless of the clock state or the J and K inputs.
• If both PR and CLR are low simultaneously, the flip-flop enters an undefined state, and its behavior is not predictable.

It’s important to note that the asynchronous inputs (PR and CLR) have priority over the synchronous inputs (J and K). If either PR or CLR is active, the flip-flop will respond to these inputs, overriding the synchronous operation.

Applications and Examples

The 74LS76 finds applications in various digital circuits, such as counters, shift registers, and control systems. Let’s explore a few practical examples to demonstrate its usage.

Example 1: Divide-by-2 Counter

A simple application of the 74LS76 is to create a divide-by-2 counter. By connecting the Q output of one flip-flop to the clock input of the next flip-flop, you can create a ripple counter that divides the input clock frequency by 2^n, where n is the number of flip-flops in the chain.

        +-------+
  CLK --| CLK1  |
        |   J1  |
        |   K1  |
        |   Q1  |--+
        | /Q1   |  |
        +-------+  |
                   |
        +-------+  |
        | CLK2  |<-+
        |   J2  |
        |   K2  |
        |   Q2  |-- Output (CLK/2)
        | /Q2   |
        +-------+

In this example, the J and K inputs of both flip-flops are connected to VCC (logic 1), causing them to toggle on each clock edge. The Q output of the first flip-flop is connected to the clock input of the second flip-flop, resulting in a divide-by-2 operation.

Example 2: Shift Register

The 74LS76 can be used to create a shift register, which is a sequential logic circuit that shifts data through a series of flip-flops. By cascading multiple 74LS76 ICs and connecting the Q output of one flip-flop to the J input of the next flip-flop, you can create an n-bit shift register.

        +-------+  +-------+  +-------+
  Data -|J1   Q1|--|J1   Q1|--|J1   Q1|----- Output
        |   CLK1|  |   CLK1|  |   CLK1|
  CLK --|>      |  |>      |  |>      |
        |   /Q1 |  |   /Q1 |  |   /Q1 |
        +-------+  +-------+  +-------+

In this example, data is shifted from left to right on each clock edge. The J inputs are used to feed the data, while the K inputs are connected to GND (logic 0) to prevent toggling. The Q outputs of each flip-flop represent the shifted data bits.

Frequently Asked Questions (FAQ)

1. What is the difference between the 74LS76 and other 74 series J-K flip-flops?
   The main difference lies in the presence of the asynchronous preset (PR) and clear (CLR) inputs in the 74LS76. Other J-K flip-flops, such as the 7476, may have different pinouts or lack the asynchronous inputs.

2. Can the 74LS76 be used as a T flip-flop?
   Yes, by connecting the J and K inputs together and using them as the T input, the 74LS76 can function as a T flip-flop. In this configuration, the flip-flop will toggle its state whenever the T input is high (logic 1) on the clock edge.

3. What happens if both PR and CLR inputs are active simultaneously?
   If both PR and CLR inputs are low (logic 0) at the same time, the flip-flop enters an undefined state, and its behavior is not predictable. It is generally advised to avoid this condition in your designs.

4. Can the 74LS76 be used in synchronous designs?
   Yes, the 74LS76 can be used in synchronous designs by utilizing the J and K inputs for synchronous operation and ensuring that the PR and CLR inputs are kept inactive (high) during normal operation.

5. What is the maximum clock frequency that the 74LS76 can handle?
   The maximum clock frequency for the 74LS76 depends on factors such as the supply voltage, load capacitance, and operating temperature. Refer to the device’s datasheet for specific timing specifications and operating conditions.

Conclusion

The 74LS76 is a versatile dual J-K flip-flop IC that finds applications in various digital circuits, including counters, shift registers, and control systems. By understanding its pinout configuration, functionality, and operating modes, you can effectively utilize the 74LS76 in your designs.

This comprehensive guide has covered the essential aspects of the 74LS76, including its pinout diagram, functional description, and practical examples. With this knowledge, you are well-equipped to incorporate the 74LS76 into your digital projects and harness its capabilities to create efficient and reliable circuits.

Remember to consult the device’s datasheet for detailed specifications, timing diagrams, and electrical characteristics to ensure proper implementation and optimal performance in your designs.