How to Use 74HC73: Examples, Pinouts, and Specs

The 74HC73 is a dual JK flip-flop integrated circuit, which is part of the 74HC family of high-speed CMOS devices. It contains two independent flip-flops with JK and negative-edge-triggered inputs. JK flip-flops are versatile and can be used in a variety of digital circuits, including counters, shift registers, and memory storage elements. The 74HC73 is commonly used in applications requiring synchronization and state storage.

• Supply Voltage (Vcc): 2.0V to 6.0V
• High-Level Input Voltage (VIH): Minimum 2.0V
• Low-Level Input Voltage (VIL): Maximum 0.8V
• Output Current (IO): ±5.2 mA
• Propagation Delay Time: Approximately 13 ns at Vcc = 4.5V, CL = 15 pF
• Operating Temperature Range: -40°C to +125°C

1. Power Supply: Connect the Vcc pin (14) to a positive supply voltage within the range of 2.0V to 6.0V. Connect the GND pin (6) to the ground of the circuit.

2. Inputs: Apply signals to the J and K inputs of the flip-flops. These inputs determine the state of the flip-flop based on the truth table.

3. Clocking: Apply a negative-edge-triggered clock pulse to the CLK input. The state of the J and K inputs is read and acted upon on the falling edge of the clock signal.

4. Outputs: The Q and \Q outputs will reflect the state of the flip-flop after the clock pulse. Q is the normal output, and \Q is the complementary output.

• Ensure that the supply voltage does not exceed the maximum rating to prevent damage to the IC.
• Unused inputs should be tied to an appropriate logic level (Vcc or GND) to avoid floating inputs, which can lead to unpredictable behavior.
• Decoupling capacitors (typically 0.1 µF) should be placed close to the Vcc pin to filter out noise and provide a stable supply voltage.
• Avoid applying inputs while the chip is not powered, as this can cause current to flow into the inputs and potentially damage the IC.

• Unstable Outputs: This can be caused by floating inputs or insufficient decoupling. Ensure all inputs are tied to a defined logic level and decoupling capacitors are used.
• No Output Change on Clock Pulse: Verify that the clock pulse is a clean falling edge and that the J and K inputs are set up correctly before the clock edge.

• Check the supply voltage and ground connections for proper levels and stability.
• Use an oscilloscope to verify the integrity of the clock signal and the timing of the J and K inputs.
• Ensure that the propagation delay of the flip-flop is accounted for in the timing of your digital circuit.

Q: Can the 74HC73 be used as a toggle flip-flop? A: Yes, by connecting the J and K inputs together and applying a high level, the flip-flop will toggle its output on each falling edge of the clock.

Q: What is the purpose of the \Q output? A: The \Q output provides the inverse of the Q output. It can be used in circuits where the complementary state is needed without additional inverting logic.

Q: How can I reset the 74HC73 flip-flops? A: The 74HC73 does not have a direct reset input. To reset the flip-flops, you must control the J and K inputs to set the desired output state on the next clock pulse.

Q: Can I chain multiple 74HC73 ICs together? A: Yes, you can chain multiple ICs to create larger sequential logic circuits. Ensure that the clock signal is distributed cleanly to all flip-flops for proper synchronization.

The following example demonstrates how to interface the 74HC73 with an Arduino UNO to toggle the state of the flip-flop with a button press.

const int buttonPin = 2; // Button connected to digital pin 2
const int clockPin = 3;  // Clock connected to digital pin 3

void setup() {
  pinMode(buttonPin, INPUT_PULLUP); // Set the button as an input with internal pull-up
  pinMode(clockPin, OUTPUT);        // Set the clock pin as an output
}

void loop() {
  static bool lastButtonState = HIGH; // Store the last state of the button
  bool currentButtonState = digitalRead(buttonPin); // Read the current state of the button

  // Check if button state has changed from HIGH to LOW (button press)
  if (lastButtonState == HIGH && currentButtonState == LOW) {
    // Generate a negative edge on the clock pin
    digitalWrite(clockPin, HIGH);
    delayMicroseconds(5); // Short delay for signal stability
    digitalWrite(clockPin, LOW);
  }

  lastButtonState = currentButtonState; // Update the last button state
}

This code sets up a simple circuit where a button press generates a clock pulse for the 74HC73 flip-flop. The J and K inputs of the flip-flop should be tied to Vcc to configure it as a toggle flip-flop. The Q output will toggle state with each button press.