## Overview of the 74FST3345DWR2 The **74FST3345DWR2** is a high-speed CMOS 8-bit bus switch manufactured by ON Semiconductor. It is primarily used to connect or isolate two different signal buses with minimal propagation delay and low "on" resistance. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Logic Type** | 8-Bit Bus Switch | | **Technology** | CMOS / FST (Fast Switch Technology) | | **Operating Voltage ($V_{CC}$)** | 4.0V to 5.5V | | **Propagation Delay** | 0.25 ns (Max) | | **On-State Resistance ($R_{on}$)** | 4 $\Omega$ (Typical) | | **Package Type** | SOIC-20 (Wide Body) | | **Operating Temperature** | -40°C to +85°C | --- ### 2. Functional Features * **Zero Propagation Delay:** Because it acts as a mechanical switch rather than a buffer, the signal passes through with almost no timing penalty. * **Bi-directional Flow:** Data can flow from Port A to Port B or vice versa without needing a direction control pin. * **Low Power Consumption:** Being a CMOS device, it draws very little current in both active and standby modes. * **High Impedance in OFF State:** When the Enable pin is set to high, the ports are completely isolated (High-Z). --- ### 3. Pinout Configuration The device is housed in a 20-pin SOIC package. Here is the functional breakdown: | Pin Name | Function | | :--- | :--- | | **$\overline{OE}$** | Output Enable (Active Low). When LOW, the switch is ON. | | **A0 - A7** | Data Port A (Inputs/Outputs) | | **B0 - B7** | Data Port B (Inputs/Outputs) | | **$V_{CC}$** | Positive Power Supply (5V) | | **GND** | Ground | --- ### 4. Typical Applications 1. **Bus Isolation:** Isolating a loaded bus from a CPU to improve signal integrity. 2. **Voltage Level Shifting:** Can be used for 5V to 3.3V translation when used with a series diode or specific $V_{CC}$ biasing. 3. **Hot-Swapping:** Protecting sensitive components during live insertion of peripheral cards. 4. **Signal Multiplexing:** Simple 1:1 switching for routing data paths. --- ### 5. Logic Diagram (Simplified) ```text OE (Pin 1/19) | ____|____ | | A0 --[Switch]-- B0 A1 --[Switch]-- B1 ... A7 --[Switch]-- B7 ```