What Is the 74HC595? Shift Register: Pinout, Operation and Uses
The 74HC595 is an 8-bit serial-in / parallel-out shift register. Using just 3 MCU pins it lets you control 8 outputs (many more when chained); it is popular for driving LEDs, 7-segment displays and relays. Data is shifted in serially, then transferred to all outputs at once with a latch (without flicker).
The 74HC595 is an 8-bit serial-in / parallel-out shift register. Using just 3 microcontroller pins it lets you control 8 outputs (many more when chained) — which is why it is so popular for driving LEDs, 7-segment displays and relays. For the concept, see what is a shift register.
What is the 74HC595 used for?
Pin saving: dozens of outputs from 3 pins. You shift data in serially, then transfer it to all outputs at once with a "latch". Because the outputs are latched into a storage register, they do not flicker while you shift. By daisy-chaining several 595s you get as many outputs as you need.
74HC595 pinout (16 pins)
| Pin | Function |
|---|---|
| 1–7 | Q1–Q7 (parallel outputs, QB–QH) |
| 8 | GND |
| 9 | Q7' (serial out — for chaining) |
| 10 | MR / SRCLR (reset, active-low) |
| 11 | SH_CP / SRCLK (shift clock) |
| 12 | ST_CP / RCLK (latch/storage clock) |
| 13 | OE (output enable, active-low) |
| 14 | DS / SER (serial data in) |
| 15 | Q0 (parallel output, QA) |
| 16 | VCC |
Note: tie OE (pin 13) to GND and MR (pin 10) to VCC (outputs on, reset inactive). Note that output Q0 is on pin 15.
How it works (summary)
- Send data bit by bit on DS (pin 14), shifting each bit in with a pulse on SRCLK (pin 11).
- Once 8 bits are in, latch them all to the outputs with a pulse on RCLK (pin 12).
- For chaining, connect Q7' (pin 9) to the DS of the next 595.
Limitations
- Current per output is limited (for high power you need a driver/transistor).
- Not for inputs (reading buttons); for that use the 74HC165 (parallel-in/serial-out).
74HC595 equivalents and alternatives
- 74HC164: a shift register without a latch.
- 74HC165: the reverse direction (parallel-in → serial-out), for reading inputs.
- TPIC6B595: a high-current (power) 595.
- MAX7219: a dedicated driver for many LEDs/7-segments.
On classic ICs: the 8 most commonly used integrated circuits.
Find it in our catalog
To compare price and stock for the 74HC595 and its alternatives, use the 74HC595 search.