74LS245 Octal bus transceiver, three-state
The 74LS245 connects two 8-bit buses in either direction. With the enable G′ low, DIR chooses the way: high passes A to B, low passes B to A. With G′ high, both sides are disconnected. Every A and B pin is both an input and an output.
74LS245 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 | DIR | Input | Input |
| 2 | A1 | Output | Three-state output |
| 3 | A2 | Output | Three-state output |
| 4 | A3 | Output | Three-state output |
| 5 | A4 | Output | Three-state output |
| 6 | A5 | Output | Three-state output |
| 7 | A6 | Output | Three-state output |
| 8 | A7 | Output | Three-state output |
| 9 | A8 | Output | Three-state output |
| 10 | GND | Ground | 0 V |
| 11 | B8 | Output | Three-state output |
| 12 | B7 | Output | Three-state output |
| 13 | B6 | Output | Three-state output |
| 14 | B5 | Output | Three-state output |
| 15 | B4 | Output | Three-state output |
| 16 | B3 | Output | Three-state output |
| 17 | B2 | Output | Three-state output |
| 18 | B1 | Output | Three-state output |
| 19 | G′ | Input | Input, active-low |
| 20 | VCC | Power | +5 V supply |
74LS245 function table
| G′ | DIR | What happens |
|---|---|---|
| 0 | 0 | B data to A |
| 0 | 1 | A data to B |
| 1 | X | Isolated: both sides disconnected |
What the 74LS245 is used for
- Buffering a bidirectional data bus
- Connecting a memory or peripheral to a shared bus
- Isolating one part of a circuit from a bus until it is needed
Electrical summary
| Package | 20-pin DIP |
| Supply voltage | 5 V (4.75 V to 5.25 V) |
| 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 3 mA |
| Input current, low | 0.4 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 74HC245 and 74HCT245 use the same pin numbers, with different electrical values.
The 74LS245 and the Breadboard Simulator
The 74LS245 is not in the Breadboard Simulator's parts library yet — this page is a reference. The simulator seats the gates, decoders, multiplexers, adders and buffers marked on the chips page, so the logic around a 74LS245 can be planned and wired there.