Overview
The SN74LS245NSR is an octal bus transceiver with 3-state outputs, designed by Texas Instruments for asynchronous two-way communication between data buses. This device utilizes Schottky transistor logic to perform the standard '245 transceiver function, featuring a common pinout, direction select pin, and active-low output enable. The SN74LS245NSR allows data transmission from the A bus to the B bus or from the B bus to the A bus, depending on the logic level at the direction-control (DIR) input. The output-enable (OE) input can disable the device, effectively isolating the buses.
Key Specifications
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| VCC (Supply Voltage) | 4.5 | 5 | 5.5 | V |
| VIH (High-level Input Voltage) | 2 | V | ||
| VIL (Low-level Input Voltage) | 0.8 | V | ||
| VOH (High-level Output Voltage) | 2.4 | 3.4 | V | |
| VOL (Low-level Output Voltage) | 0.4 | 0.5 | V | |
| tPLH (Propagation Delay Time, Low to High) | 8 | 12 | ns | |
| tPHL (Propagation Delay Time, High to Low) | 8 | 12 | ns | |
| tPZL (Output Enable Time to Low Level) | 27 | 40 | ns | |
| tPZH (Output Enable Time to High Level) | 25 | 40 | ns |
Key Features
- 3-State Outputs: The outputs can drive bus lines directly and can be put into high impedance mode through the OE pin.
- PNP Inputs: Reduce DC loading on bus lines.
- Hysteresis on Bus Inputs: Improves noise margins.
- Direction Control: Data transmission can be controlled from A bus to B bus or from B bus to A bus using the DIR input.
- Output Enable: The OE input can disable the device, isolating the buses.
- Propagation Delay: Typical propagation delay times of 8 ns.
Applications
- Building Automation: Used in control and communication systems.
- Electronic Point of Sale: Enhances data transmission reliability.
- Factory Automation and Control: Ideal for industrial control systems.
- Test and Measurement: Used in various test equipment and measurement devices.
- Ribbon Cables and Back Plane Buses: Increases drive strength and allows isolation from the bus when necessary.
Q & A
- What is the primary function of the SN74LS245NSR?
The primary function is to enable asynchronous two-way communication between data buses.
- How does the direction of data transmission in the SN74LS245NSR get controlled?
Data transmission direction is controlled by the logic level at the direction-control (DIR) input.
- What is the purpose of the OE input in the SN74LS245NSR?
The OE input can disable the device, effectively isolating the buses.
- What are the typical propagation delay times for the SN74LS245NSR?
Typical propagation delay times are 8 ns for both low to high and high to low transitions.
- What is the significance of hysteresis on bus inputs in the SN74LS245NSR?
Hysteresis on bus inputs improves noise margins.
- What are the recommended operating conditions for the supply voltage of the SN74LS245NSR?
The supply voltage should be between 4.5 V and 5.5 V.
- How does the SN74LS245NSR handle output enable and disable times?
The output enable time to low level is typically 27-40 ns, and the output enable time to high level is typically 25-40 ns.
- What types of applications benefit from using the SN74LS245NSR?
Applications include building automation, electronic point of sale, factory automation, test and measurement, and driving ribbon cables or back plane buses.
- What is the significance of PNP inputs in the SN74LS245NSR?
PNP inputs reduce DC loading on bus lines.
- How should the power supply be managed for the SN74LS245NSR?
Each VCC pin should have a good bypass capacitor to prevent power disturbance. Typically, a 0.1-µF bypass capacitor is recommended.
