74LS244 Octal buffer / line driver, three-state
The 74LS244 is an octal buffer and line driver with three-state outputs, arranged as two groups of four. Each group has its own active-low enable: with the enable low the four outputs follow their inputs, and with it high they are disconnected (high impedance). Its outputs drive far more current than an ordinary gate.
74LS244 pinout
Top view of the 20-pin DIP package. Pin 1 is at the bottom left, beside the notch, and the numbers run anticlockwise. Power is on pin 20 (VCC, +5 V) and pin 10 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | 1G′ | Input | Input, active-low |
| 2 | 1A1 | Input | Input |
| 3 | 2Y4 | Output | Three-state output |
| 4 | 1A2 | Input | Input |
| 5 | 2Y3 | Output | Three-state output |
| 6 | 1A3 | Input | Input |
| 7 | 2Y2 | Output | Three-state output |
| 8 | 1A4 | Input | Input |
| 9 | 2Y1 | Output | Three-state output |
| 10 | GND | Ground | 0 V |
| 11 | 2A1 | Input | Input |
| 12 | 1Y4 | Output | Three-state output |
| 13 | 2A2 | Input | Input |
| 14 | 1Y3 | Output | Three-state output |
| 15 | 2A3 | Input | Input |
| 16 | 1Y2 | Output | Three-state output |
| 17 | 2A4 | Input | Input |
| 18 | 1Y1 | Output | Three-state output |
| 19 | 2G′ | Input | Input, active-low |
| 20 | VCC | Power | +5 V supply |
74LS244 function table
| G′ | A | Y |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | X | Z |
X is either value. Z is high impedance: the output is disconnected.
What the 74LS244 is used for
- Driving a bus or a long line
- Buffering address and data lines
- Putting a set of switches or sensors onto a shared data bus
- Eight plain buffers, with both enables tied low
The line driver the decoder documentation puts on the distribution bus: 15 mA out high and 24 mA in low, where a plain gate manages 0.4 and 8. Tie both enables low to use it as eight plain buffers.
Electrical summary
| Package | 20-pin DIP |
| Supply voltage | 5 V (4.75 V to 5.25 V) |
| Supply current, typical | 25 mA |
| Output type | Three-state — drives high and low, or disconnects when disabled |
| Output current, low | sinks up to 24 mA |
| Output current, high | sources up to 15 mA |
| Input current, low | 0.2 mA out of each input held low |
| Fan-out | one output can drive about 60 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 74HC244 and 74HCT244 use the same pin numbers, with different electrical values.
Try the 74LS244 on a breadboard
The Breadboard Simulator has the 74LS244 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.