Onsemi MC74HC165ADTR2G: 8-Bit Parallel-Load Shift Register Datasheet and Application Guide

The MC74HC165ADTR2G from Onsemi is a high-performance, 8-bit parallel-load shift register belonging to the 74HC high-speed CMOS logic family. This integrated circuit is designed to efficiently convert parallel data into a serial output stream, making it an indispensable component in applications where minimizing microcontroller pin count is critical or where data must be transmitted over long distances. Housed in a space-saving TSSOP-16 package, it is ideal for modern, compact electronic designs.

Key Features and Electrical Characteristics

The device operates over a broad voltage range of 2.0 V to 6.0 V, ensuring compatibility with various logic levels, including 3.3V and 5V systems. It features low power consumption typical of HC logic technology, with a maximum static current of just 4 µA. The high-noise immunity of CMOS technology makes it robust in electrically noisy environments.

Its core functionality includes an asynchronous parallel load capability. When the Parallel Load (PL) input is driven low, the data present at the eight parallel inputs (D0 to D7) is loaded into the register independently of the clock signals. When PL is high, the device shifts data on each rising edge of the clock. It features a gated clock input (CP) and a complementary clock enable (CE) that allows for easy clock management. A separate serial data input (DS) enables cascading multiple devices to form longer shift registers without additional logic.

Application Guide and Circuit Implementation

A primary application for the MC74HC165 is digital input expansion for microcontrollers. A single MC74HC165 can read eight digital signals using only three microcontroller GPIO pins (for data, clock, and load control). By daisy-chaining multiple registers, the number of inputs can be expanded almost indefinitely while still using only three controller pins.

A typical connection diagram involves:

1. Connecting all parallel inputs (D0-D7) to the signals to be monitored (e.g., switches, sensors).

2. Connecting the Serial Output (Q7) to a microcontroller's digital input pin.

3. Connecting the Clock (CP) and Parallel Load (PL) pins to two other microcontroller output pins.

4. The Clock Enable (CE) is typically tied low to enable the clock.

The data reading process follows a simple sequence:

1. The microcontroller pulses the PL pin low, then high. This latches the current state of all eight parallel inputs into the internal register.

2. The microcontroller then pulses the clock pin high eight times. On each rising edge, the bits are shifted, and the value of the first bit (D0) appears at the serial output (Q7) after the first clock pulse. The microcontroller reads this serial data stream on its input pin, reconstructing the complete 8-bit byte.

This device is also widely used in applications such as industrial control systems for monitoring multiple switch banks, in data acquisition systems, and for controlling LED matrices.

ICGOOODFIND: The Onsemi MC74HC165ADTR2G is a highly efficient and reliable solution for parallel-to-serial data conversion and input expansion. Its low power consumption, wide operating voltage range, and ease of cascading make it a versatile choice for designers looking to optimize system cost and pin efficiency across a wide array of digital applications.

Keywords: Parallel-to-Serial Converter, Input Expansion, Shift Register, 74HC Logic, Daisy-Chaining.