74HC138 Pinout

74HC138 3-to-8 Decoder · 3-to-8 line decoder (active-low outputs); commonly used for address decoding / chip select.

DIP-16 Logic 16 pins No backend · 100% client-side

A0(A) 1

A1(B) 2

A2(C) 3

E1(/G2A) 4

E2(/G2B) 5

E3(G1) 6

Y7 7

GND 8

74HC138 DIP-16

16 VCC

15 Y0

14 Y1

13 Y2

12 Y3

11 Y4

10 Y5

9 Y6

PowerGNDInputOutputI/OControl

Pin	Name	Type	Function
1	A0 · A	Input	Address input bit0 (LSB)
2	A1 · B	Input	Address input bit1
3	A2 · C	Input	Address input bit2 (MSB)
4	E1 · /G2A	Control	Enable (active-low)
5	E2 · /G2B	Control	Enable (active-low)
6	E3 · G1	Control	Enable (active-high)
7	Y7	Output	Output 7 (active-low)
8	GND	GND	Ground
9	Y6	Output	Output 6 (active-low)
10	Y5	Output	Output 5 (active-low)
11	Y4	Output	Output 4 (active-low)
12	Y3	Output	Output 3 (active-low)
13	Y2	Output	Output 2 (active-low)
14	Y1	Output	Output 1 (active-low)
15	Y0	Output	Output 0 (active-low)
16	VCC	Power	Supply + (2–6V)

How to · reading it

How to read the 74HC138 pinout

01
Find pin 1
One end of the chip has a half-circle notch or a dot; with the notch facing up, the top-left pin is pin 1.
02
Count counter-clockwise
Count counter-clockwise from pin 1: go down the left side first, then up the right side from the bottom.
03
Check the table below
Look up each pin's function by number in the table below; power/ground are color-coded, and alternate-function signals are in parentheses.

FAQ

How do I use the three enable pins?

It only operates when E1=0, E2=0, and E3=1 are all satisfied; if any one fails, all outputs go high (inactive). This can be used to extend decoding.

Why are the outputs active-low?

The selected output goes to 0 and the rest stay at 1. For chip select (CS) this maps perfectly onto active-low memory/peripherals.

Data source

Pinout data comes from NXP/TI 74HC138 datasheet (standard DIP-16 numbering). Refer to the actual device datasheet as authoritative for the pinout.