SCEA117 July   2022 SN74HCS164 , SN74HCS164-Q1 , SN74HCS165 , SN74HCS165-Q1 , SN74HCS595 , SN74HCS595-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Overview
    1. 1.1 Types of Shift Registers
    2. 1.2 Default State of a Shift Register
    3. 1.3 164 Function Shift Registers
    4. 1.4 165 Function Shift Registers
    5. 1.5 595 Function Shift Registers
    6. 1.6 Daisy-Chain Two Shift Registers
  4. 2Design Challenges
    1. 2.1 Controller Loading Limits
    2. 2.2 Operating over Large Distances
    3. 2.3 Data Loss Due to Signal Timing
    4. 2.4 Data Rate Limitations
    5. 2.5 Software Overview
  5. 3Example Design - Daisy Chain 72 Shift Registers
    1. 3.1 System Overview
    2. 3.2 System Design
    3. 3.3 Software Examples
  6. 4References

Abstract

Shift registers provide a simple, low cost, and flexible method for increasing the total number of input or output (IO) pins on a system controller. The fact that shift registers can be connected in series, or daisy-chained together, means that very few IO pins are required to support a large number of devices. The only two real caveats for their use are that they cannot provide a significant amount of power directly, and the IO signals must be much slower than the system clock.

Stepper motors require multiple relatively slow input signals that can be controlled through shift registers so long as the power for driving the motors comes from separate dedicated drivers. Appliances such as air conditioners, washers, dryers, and refrigerators commonly use stepper motors that benefit from shift registers. Industrial electronics such as servo motor drive controls for multi- or single-axis motors utilize shift registers for the same reasons.

It is also common to see shift registers in user interfaces for both LED control and keypad polling since humans are generally able to discern differences only on the millisecond time scale. Medical applications such as oxygen concentrators utilize shift registers for monitoring keys and lighting indicators. Similarly, fire control panels and elevator control panels commonly use shift registers for LED outputs and button inputs.

This document provides a complete description of the most common shift register functions (164, 165, 595), an explanation of how each common function operates, key design concepts to prevent issues when using them, and an example system design utilizing existing parts.