The **FST3244WMX** is a high-speed CMOS bus switch manufactured by Fairchild (now part of ON Semiconductor). It is designed for high-performance systems where low power consumption and high-speed data switching are critical. ### 1. General Overview The FST3244 belongs to the Fairchild Switch Technology (FST) family. It consists of two 4-bit switches (totaling 8 bits) with separate output-enable ($\overline{OE}$) controls. When the output enable is LOW, the switch is closed, allowing bi-directional communication between ports. ### 2. Technical Specifications | Parameter | Value | Description | | :--- | :--- | :--- | | **Supply Voltage ($V_{CC}$)** | 4.0V to 5.5V | Typical operating range | | **Propagation Delay** | 0.25 ns | Near-zero delay through the switch | | **On Resistance ($R_{ON}$)** | 4$\Omega$ to 8$\Omega$ | Extremely low resistance to minimize signal distortion | | **Input/Output Capacitance** | 5pF to 10pF | Low loading on the bus | | **Package Type** | SOIC-20 | 20-pin Small Outline Integrated Circuit | | **Packing Method** | Tape and Reel (X) | Indicated by the 'X' in the suffix | --- ### 3. Pin Configuration and Functions The device is organized as two sets of 4-bit switches. * **1A1 - 1A4 / 2A1 - 2A4:** Port A inputs/outputs. * **1B1 - 1B4 / 2B1 - 2B4:** Port B inputs/outputs. * **$\overline{1OE}$ / $\overline{2OE}$:** Active LOW Output Enable pins. * **GND / $V_{CC}$:** Power supply pins. ### 4. Key Features and Logic The FST3244 acts essentially like a mechanical relay but at semiconductor speeds. It does not generate drive strength; it simply connects two nodes. 1. **Low $R_{ON}$:** Prevents voltage drops across the switch. 2. **Bi-directional:** Signals can flow from A to B or B to A. 3. **High Impedance in OFF State:** When $\overline{OE}$ is HIGH, the ports are isolated. 4. **Zero Propagation Delay:** Because it is a simple FET switch, it doesn't wait for a clock or logic transition to pass the signal. --- ### 5. Common Applications * **Bus Isolation:** Separating different segments of a computer bus to reduce capacitive loading. * **Voltage Translation:** Can be used for 5V to 3.3V level shifting (when used with a diode or specific $V_{CC}$ bias). * **Hot-Plugging:** Protecting sensitive circuitry during live insertion of peripheral cards. * **Memory Interfacing:** Switching between different banks of memory or processors. --- ### 6. Package Information (WMX Suffix) The suffix **WMX** provides specific details about the physical form: * **WM:** Indicates a Wide Body SOIC (Small Outline Integrated Circuit). * **X:** Indicates that the parts are shipped in **Tape and Reel** format for automated assembly.