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74HC595 Shift Register

An 8-bit serial-in, parallel-out shift register primarily used to massively expand the number of digital outputs on a microcontroller.

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74HC595

The 74HC595 is one of the most famous ICs in the maker community. It allows you to control 8 separate outputs (like LEDs, relays, or 7-segment displays) using just 3 pins on your microcontroller. Like the 165, multiple 595 chips can be daisy-chained together to control 16, 24, or even 100+ outputs from those same 3 pins.

Logic ComponentsShift RegisterOutput Expansion

Overview

Where the 74HC165 takes multiple inputs and collapses them into one serial line, the 74HC595 does the exact reverse: it takes a single serial line and expands it into 8 parallel outputs. It contains both a shift register (which receives data bit by bit) and a storage register (which holds the data steady on the output pins).

Pin Reference

Pin	Type	Description
VCC	power	Power supply (3V to 5V).
GND	power	Ground reference.
Q0-Q7	digital	The 8 parallel outputs. (Pins 15, and 1-7).
SER	input	Serial Input (DS). The pin where you send data bits one at a time.
SRCLK	input	Shift Register Clock (SHCP). Shifts data from SER into the internal memory on the rising edge.
RCLK	input	Storage Register Clock (STCP or Latch). Transfers data from the internal shift register to the output pins (Q0-Q7) on the rising edge.
SRCLR	input	Master Reclear (MR). Active LOW. Clears the shift register when tied to GND. Usually tied to VCC.
OE	input	Output Enable. Active LOW. Disables all outputs (high impedance) when HIGH. Usually tied to GND.
Q7S	digital	Serial Output. Used for daisy-chaining. Connect to the SER pin of the next 74HC595.

Configurable Attributes

This component currently has no configurable attributes in the simulator.

Working Principle

1. Shift Phase: You present a bit (HIGH or LOW) on the SER pin and pulse the SRCLK pin HIGH then LOW. The bit enters the shift register. You repeat this 8 times for all 8 bits.
2. Latch Phase: Once all 8 bits are in the shift register, you pulse the RCLK (Latch) pin HIGH then LOW. This copies the 8 bits simultaneously to the visible output pins (Q0-Q7).
3. Daisy Chaining: As you shift more than 8 bits into a single chip, the oldest bits "spill out" of the Q7S pin. By connecting Q7S to the SER pin of a second 595, the bits automatically flow into the second chip!

Wiring Diagram

Example of connecting a 74HC595 Shift Register to an Arduino Uno.

Example Arduino Code

The Arduino shiftOut function is designed specifically for this chip.

const int dataPin  = 11; // SER
const int clockPin = 12; // SRCLK
const int latchPin = 8;  // RCLK

void setup() {
  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(latchPin, OUTPUT);
}

void loop() {
  // We will count from 0 to 255 and display it in binary on the outputs
  for (int i = 0; i < 256; i++) {
    // 1. Pull latch LOW to keep outputs steady while shifting
    digitalWrite(latchPin, LOW);
    
    // 2. Shift all 8 bits in
    shiftOut(dataPin, clockPin, MSBFIRST, i);
    
    // 3. Pull latch HIGH to push the bits to the outputs
    digitalWrite(latchPin, HIGH);
    
    delay(100);
  }
}

Simulation Notes

• The simulator visually represents the state of the internal registers and outputs instantly.
• If you cascade multiple 595s in the simulator, simply use shiftOut multiple times before pulling the latch pin high. (e.g., call shiftOut twice to control 16 LEDs).

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