74LS157 Quad 2-to-1 multiplexer
The 74LS157 holds four 2-to-1 multiplexers with a common select S and a common active-low enable G′. With S low, every output Y follows its A input; with S high, its B input. With G′ high, all four outputs are low.
74LS157 pinout
Top view of the 16-pin DIP package. Pin 1 is at the bottom left, beside the notch, and the numbers run anticlockwise. Power is on pin 16 (VCC, +5 V) and pin 8 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | S | Input | Input |
| 2 | 1A | Input | Input |
| 3 | 1B | Input | Input |
| 4 | 1Y | Output | Totem-pole output |
| 5 | 2A | Input | Input |
| 6 | 2B | Input | Input |
| 7 | 2Y | Output | Totem-pole output |
| 8 | GND | Ground | 0 V |
| 9 | 3Y | Output | Totem-pole output |
| 10 | 3B | Input | Input |
| 11 | 3A | Input | Input |
| 12 | 4Y | Output | Totem-pole output |
| 13 | 4B | Input | Input |
| 14 | 4A | Input | Input |
| 15 | G′ | Input | Input, active-low |
| 16 | VCC | Power | +5 V supply |
74LS157 function table
| G′ | S | Y |
|---|---|---|
| 1 | X | 0 |
| 0 | 0 | A |
| 0 | 1 | B |
X is either value.
What the 74LS157 is used for
- Switching a 4-bit bus between two sources
- Choosing between two operands ahead of an adder
- Implementing four simple functions of the select and two data inputs
Electrical summary
| Package | 16-pin DIP |
| Supply voltage | 5 V (4.75 V to 5.25 V) |
| Supply current, typical | 9.7 mA |
| Output type | Totem-pole — drives both high and low |
| Output current, low | sinks up to 8 mA |
| Output current, high | sources up to 0.4 mA |
| Input current, low | 0.4 mA out of each input held low |
| Fan-out | one output can drive about 20 LS inputs |
Typical figures for quick reference when planning a board. Check the manufacturer's datasheet for limits and timing before committing a design. The 74HC157 and 74HCT157 use the same pin numbers, with different electrical values.
Try the 74LS157 on a breadboard
The Breadboard Simulator has the 74LS157 in its parts library: seat it on a virtual breadboard, wire it, power the board and probe the pins before you build the real thing.