74240 IC Octal Buffer/Line Driver (3-State)
The IC 74240 is an octal buffer and line driver with active-low enable inputs and 3-state outputs. It contains eight independent buffers arranged as two groups of four. Each group has its own enable input, allowing selective control.
When an enable input is LOW, the corresponding group drives its outputs to match the inputs. When the enable input is HIGH, the outputs enter a high-impedance (Hi-Z) state, effectively disconnecting them from the bus. This feature makes the 74240 suitable for bus-oriented applications, preventing multiple devices from driving the same bus simultaneously.
Its TTL-compatible design and ability to source and sink significant current make it useful for signal buffering, bus driving, and data isolation in high-speed digital circuits.
Pin Configuration (DIP-20)
| Pin | Name | Description |
|---|---|---|
| 1 | 1OE¯ | Output Enable for 1Y1–1Y4 (LOW = active) |
| 2 | 1A1 | Input 1 |
| 3 | 2Y4 | Output 4 (Group 2) |
| 4 | 1A2 | Input 2 |
| 5 | 2Y3 | Output 3 (Group 2) |
| 6 | 1A3 | Input 3 |
| 7 | 2Y2 | Output 2 (Group 2) |
| 8 | 1A4 | Input 4 |
| 9 | 2Y1 | Output 1 (Group 2) |
| 10 | GND | Ground |
| 11 | 2OE¯ | Output Enable for 2Y1–2Y4 (LOW = active) |
| 12 | 2A1 | Input 1 (Group 2) |
| 13 | 1Y4 | Output 4 (Group 1) |
| 14 | 2A2 | Input 2 (Group 2) |
| 15 | 1Y3 | Output 3 (Group 1) |
| 16 | 2A3 | Input 3 (Group 2) |
| 17 | 1Y2 | Output 2 (Group 1) |
| 18 | 2A4 | Input 4 (Group 2) |
| 19 | 1Y1 | Output 1 (Group 1) |
| 20 | VCC | +5V Power Supply |
Key Features
Eight non-inverting buffers/drivers
3-state outputs for bus-oriented designs
Two independent enable controls
High output drive capability
TTL-compatible input/output levels
Available in DIP-20 and SOIC-20 packages
Applications
Drive data buses in microprocessor systems.
Isolate signals between subsystems.
Buffer control signals for long transmission lines.
Reduce loading on logic outputs.
Enable bidirectional bus communication with external gating.
Expand fan-out for digital circuits.
Build memory interface buffers.
Use as an output stage for peripheral devices.
Implement address/data multiplexing.
Control data flow in multi-board systems.
Specifications Table
| Parameter | Value |
|---|---|
| Logic Family | TTL |
| Function | Octal Buffer/Driver |
| Number of Buffers | 8 |
| Output State | 3-state |
| Input HIGH Voltage | ≥ 2.0V |
| Input LOW Voltage | ≤ 0.8V |
| Output HIGH Voltage | ≥ 2.4V |
| Output LOW Voltage | ≤ 0.4V |
| Propagation Delay | ~12 ns ‘ |
| Max Output Current | ±24 mA |
| Supply Voltage | 4.75V to 5.25V |
| Max Clock Frequency | Not clocked |
| Operating Temp | 0°C to 70°C |
| Package Type | DIP-20 / SOIC-20 |
| Number of Pins | 20 |
