## Overview of FST16233 The **FST16233** is a high-speed CMOS TTL-compatible 16-bit to 32-bit **Multiplexer/Demultiplexer Bus Switch**. It is primarily designed to provide a high-speed, low-propagation-delay connection between two buses or as a switching fabric in high-performance computing systems. --- ### Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Logic Family** | FST (Bus Switch) | | **Configuration** | 16-bit to 32-bit (1-of-2) | | **Supply Voltage ($V_{CC}$)** | 4.0V to 5.5V | | **On-State Resistance ($R_{on}$)** | Typically 4Ω to 8Ω | | **Propagation Delay** | < 0.25 ns (Near Zero) | | **Package Options** | TSSOP, SSOP | --- ### Functional Breakdown #### 1. Pin Configuration and Architecture The device is organized as a 16-bit 1-of-2 multiplexer. This means there are 16 "common" pins that can be routed to one of two sets of 16-bit outputs/inputs. * **A Port:** 16-bit common bus. * **B Port:** Two sets of 16-bit buses ($B_1$ and $B_2$). * **Control Pins:** Select ($S$) and Output Enable ($\overline{OE}$). #### 2. The Bus Switch Principle Unlike a standard logic gate (like a buffer or AND gate), the FST16233 acts as a **Voltage-Controlled Resistor**. * When the switch is **ON**, the A and B ports are connected via a very low-resistance path. * When the switch is **OFF**, the ports are in a High-Impedance (Hi-Z) state. #### 3. Low Propagation Delay Because it uses an N-Channel MOSFET as the switching element, it does not add significant propagation delay (it does not re-drive the signal). The only delay added is the $RC$ time constant formed by the $R_{on}$ of the switch and the load capacitance. --- ### Truth Table The operation is controlled by the Select ($S$) and Output Enable ($\overline{OE}$) pins: | $\overline{OE}$ | $S$ | Function | | :---: | :---: | :--- | | L | L | A Port connected to $B_1$ Port | | L | H | A Port connected to $B_2$ Port | | H | X | Disconnected (High Impedance) | --- ### Common Applications 1. **Memory Interleaving:** Switching a CPU address/data bus between two different banks of RAM. 2. **Bus Isolation:** Hot-swapping applications where a sub-system needs to be physically isolated from the main bus to prevent noise or damage. 3. **Signal Multiplexing:** Reducing the number of traces required on a PCB by sharing a bus between multiple peripherals. 4. **Voltage Level Translation:** When used with a diode or specific $V_{CC}$ settings, it can provide basic 5V to 3.3V translation. --- ### Example Schematic Implementation ```c // Conceptual logic flow for FST16233 Control if (OE_Low) { if (Select == 0) { Path = A_to_B1; // Transparent connection } else { Path = A_to_B2; // Transparent connection } } else { Path = Open_Circuit; // All ports isolated } ```