74HC139 Pinout
74HC139 Dual 2-to-4 Decoder · Dual 2-to-4 line decoder (active-low outputs), each with its own enable.
| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | 1E · /1E | Control | Decoder 1 enable (active-low) |
| 2 | 1A0 · 1A | Input | Decoder 1 address bit0 |
| 3 | 1A1 · 1B | Input | Decoder 1 address bit1 |
| 4 | 1Y0 | Output | Decoder 1 output 0 (active-low) |
| 5 | 1Y1 | Output | Decoder 1 output 1 |
| 6 | 1Y2 | Output | Decoder 1 output 2 |
| 7 | 1Y3 | Output | Decoder 1 output 3 |
| 8 | GND | GND | Ground |
| 9 | 2Y3 | Output | Decoder 2 output 3 (active-low) |
| 10 | 2Y2 | Output | Decoder 2 output 2 |
| 11 | 2Y1 | Output | Decoder 2 output 1 |
| 12 | 2Y0 | Output | Decoder 2 output 0 |
| 13 | 2A1 · 2B | Input | Decoder 2 address bit1 |
| 14 | 2A0 · 2A | Input | Decoder 2 address bit0 |
| 15 | 2E · /2E | Control | Decoder 2 enable (active-low) |
| 16 | VCC | Power | Supply + (2–6V) |
How to read the 74HC139 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.
Frequently asked questions
Difference from the 74HC138?
The 138 is a single 3-to-8 decoder; the 139 is two independent 2-to-4 decoders (each with its own enable), suiting separate chip-select for two groups.
How do I use the enable pins?
/E is active-low: low = active (the selected output goes low, the rest high), high = all outputs high (disabled).
Pinout data comes from NXP/TI 74HC139 datasheet (standard DIP-16 numbering). Refer to the actual device datasheet as authoritative for the pinout.