How to Use 74ls173: Examples, Pinouts, and Specs

Introduction

The 74LS173 is a quad D-type flip-flop manufactured by Texas Instruments. It features four D-type flip-flops with a common clock input and active-low enable inputs. This component is widely used in digital circuits for data storage and transfer, enabling the synchronization of data with a clock signal. Its compact design and reliable performance make it a popular choice in applications requiring temporary data storage or controlled data flow.

Explore Projects Built with 74ls173

LED Control Circuit with 7408 AND Gate and 74HC75 Latch

This circuit is a simple logic-based LED control system. It uses a 7408 AND gate and a 74HC75 latch to control the state of a red LED based on the input from three push switches. The BC547 transistor acts as a switch to drive the LED, with resistors used for current limiting and biasing.

Open Project in Cirkit Designer

74HC74 and 7408 Based LED Control Circuit with Push Switches

This circuit is a simple flip-flop based LED control system. It uses a 74HC74 D flip-flop to toggle the state of an LED, with push switches to control the clock and data inputs. The circuit also includes a 7408 AND gate and a BC547 transistor to drive the LED.

Open Project in Cirkit Designer

74HC4017-Based Sequential LED Flasher with Pushbutton Control

This circuit includes a decade counter (74HC4017) that likely sequences through outputs based on pushbutton inputs. A BC547 transistor is used to drive an LED, indicating one of the counter's states. Diodes and resistors are included for current direction control and limiting, respectively.

Open Project in Cirkit Designer

Portable Decade Counter Circuit with LED Indicator and Pushbutton Control

This circuit uses a 74HC4017 decade counter to control the sequence of an LED array. Pushbuttons are used to interact with the counter, advancing or resetting the sequence, while a BC547 transistor is used to switch an LED on and off. Diodes are included to prevent reverse current, ensuring proper operation of the counter.

Open Project in Cirkit Designer

Common Applications

Data latching and storage in digital systems
Buffering and synchronization of data
Shift registers and counters
Memory addressing and control logic

Technical Specifications

The following table outlines the key technical details of the 74LS173:

Parameter	Value
Supply Voltage (Vcc)	4.75V to 5.25V
Input Voltage (VI)	0V to 7V
High-Level Output Voltage	2.7V (min)
Low-Level Output Voltage	0.4V (max)
High-Level Input Current	20 µA (max)
Low-Level Input Current	-0.4 mA (max)
Propagation Delay (typical)	20 ns
Operating Temperature Range	0°C to 70°C
Package Type	DIP-16, SOIC-16

Pin Configuration and Descriptions

The 74LS173 comes in a 16-pin package. The pinout and descriptions are as follows:

Pin Number	Pin Name	Description
1	MR	Master Reset (Active Low)
2	G1	Enable Input 1 (Active Low)
3	G2	Enable Input 2 (Active Low)
4	D0	Data Input 0
5	D1	Data Input 1
6	D2	Data Input 2
7	D3	Data Input 3
8	GND	Ground
9	Q3	Data Output 3
10	Q2	Data Output 2
11	Q1	Data Output 1
12	Q0	Data Output 0
13	CLK	Clock Input
14	OE1	Output Enable 1 (Active Low)
15	OE2	Output Enable 2 (Active Low)
16	Vcc	Positive Supply Voltage

Usage Instructions

The 74LS173 is straightforward to use in digital circuits. Below are the steps and considerations for proper usage:

Basic Circuit Connection

Power Supply: Connect pin 16 (Vcc) to a 5V power supply and pin 8 (GND) to ground.
Clock Signal: Provide a clock signal to pin 13 (CLK) to synchronize data storage and transfer.
Data Inputs: Connect the data inputs (D0–D3) to the desired data source.
Enable Inputs: Ensure that both enable inputs (G1 and G2) are held low to enable the flip-flops.
Output Enable: To activate the outputs (Q0–Q3), set both OE1 and OE2 to low. If either is high, the outputs will be in a high-impedance state.
Master Reset: Use the MR pin to reset all outputs to low. This pin is active low, so it must be held high during normal operation.

Example Circuit with Arduino UNO

The 74LS173 can be interfaced with an Arduino UNO for data storage and control. Below is an example code snippet:

// Example: Interfacing 74LS173 with Arduino UNO
// This code demonstrates how to control the 74LS173 flip-flop using Arduino.

// Pin definitions
const int clkPin = 2;  // Clock signal
const int mrPin = 3;   // Master Reset
const int g1Pin = 4;   // Enable Input 1
const int g2Pin = 5;   // Enable Input 2
const int dPins[] = {6, 7, 8, 9}; // Data inputs D0-D3

void setup() {
  // Set pin modes
  pinMode(clkPin, OUTPUT);
  pinMode(mrPin, OUTPUT);
  pinMode(g1Pin, OUTPUT);
  pinMode(g2Pin, OUTPUT);
  for (int i = 0; i < 4; i++) {
    pinMode(dPins[i], OUTPUT);
  }

  // Initialize pins
  digitalWrite(mrPin, HIGH);  // Disable reset
  digitalWrite(g1Pin, LOW);   // Enable flip-flops
  digitalWrite(g2Pin, LOW);   // Enable flip-flops
  digitalWrite(clkPin, LOW);  // Initialize clock
}

void loop() {
  // Example: Store and transfer data
  for (int i = 0; i < 16; i++) {
    // Set data inputs
    for (int j = 0; j < 4; j++) {
      digitalWrite(dPins[j], (i >> j) & 0x01); // Set each bit of D0-D3
    }

    // Generate clock pulse
    digitalWrite(clkPin, HIGH);
    delay(10); // Short delay for clock pulse
    digitalWrite(clkPin, LOW);
    delay(10);
  }
}

Best Practices

Use decoupling capacitors (e.g., 0.1 µF) near the Vcc pin to reduce noise and ensure stable operation.
Avoid floating inputs by connecting unused inputs to a defined logic level (e.g., GND or Vcc).
Ensure the clock signal is clean and free of noise to prevent unintended behavior.

Troubleshooting and FAQs

Common Issues

Outputs Not Responding:
- Check if the enable inputs (G1 and G2) are both low.
- Verify that the output enable pins (OE1 and OE2) are low.
- Ensure the clock signal is properly connected and functioning.
Unexpected Output States:
- Confirm that the data inputs (D0–D3) are correctly set before the clock pulse.
- Check for noise or glitches on the clock line.
Outputs Stuck in High-Impedance:
- Verify that both OE1 and OE2 are low. If either is high, the outputs will be disabled.

FAQs

Q1: Can the 74LS173 operate at 3.3V?
No, the 74LS173 is designed to operate within a supply voltage range of 4.75V to 5.25V. Using it at 3.3V may result in unreliable operation.

Q2: What happens if the MR pin is left floating?
The MR pin is active low and should not be left floating. If left unconnected, it may cause unpredictable behavior. Connect it to Vcc for normal operation or to GND to reset the outputs.

Q3: How do I cascade multiple 74LS173 ICs?
To cascade multiple ICs, connect the clock and enable inputs in parallel. Use the outputs of one IC as the inputs to the next stage for extended data storage or transfer.

By following this documentation, users can effectively integrate the 74LS173 into their digital circuits for reliable data storage and synchronization.