The **U74CBT3257G-R16-R** is a high-speed CMOS 4-bit 1-of-2 multiplexer/demultiplexer (bus switch). It is designed for high-performance applications where low propagation delay and bidirectional data flow are critical. ### 1. General Specifications This part functions as a high-speed TTL-compatible FET bus switch. When enabled, the switch is closed, allowing data to flow with minimal resistance. | Parameter | Description | | :--- | :--- | | **Device Type** | 4-Bit 1-of-2 Multiplexer/Demultiplexer | | **Logic Family** | CBT (Crossbar Technology) | | **Voltage Supply Range** | 4.0V to 5.5V | | **Input/Output Type** | TTL Compatible / Bidirectional | | **Packaging** | SSOP-16 / TSSOP-16 (Depending on R16 suffix) | | **Ron (On-Resistance)** | ~5Ω (Typical) | --- ### 2. Functional Description The device consists of four independent 2:1 switches. It uses a Select ($S$) input to determine which port is connected to the common port, and an Output Enable ($\overline{OE}$) pin to activate or isolate the bus. #### Truth Table | $\overline{OE}$ Input | $S$ Input | Function | | :---: | :---: | :--- | | L | L | Port A connected to Port B1 | | L | H | Port A connected to Port B2 | | H | X | Disconnect (High-Z State) | --- ### 3. Key Technical Features * **Zero Propagation Delay:** Because it uses a FET switch rather than a logic buffer, there is no inherent propagation delay added to the signal (other than the RC delay of the On-resistance). * **Bidirectional Operation:** Data can flow from common to individual ports or vice versa without needing a direction control pin. * **Low On-Resistance:** Typically $5\Omega$, ensuring minimal voltage drop across the switch. * **Hot Insertion Capable:** The device supports "live" insertion or removal without damaging the bus or the IC. --- ### 4. Application Circuit Example In a typical application, this chip is used to route a 4-bit bus between two different peripherals (like two different memory modules or sensors). ```c // Pseudo-Logic for controlling the U74CBT3257 via GPIO void select_channel(int channel) { if (channel == 1) { digitalWrite(PIN_S, LOW); // Route A to B1 } else { digitalWrite(PIN_S, HIGH); // Route A to B2 } digitalWrite(PIN_OE, LOW); // Enable Switch } ``` --- ### 5. Common Use Cases 1. **Bus Isolation:** Isolating a segment of a bus to reduce capacitive loading. 2. **Memory Interleaving:** Switching data lines between two banks of SDRAM or Flash. 3. **Voltage Level Shifting:** Can be used for 5V to 3.3V translation if the input is clamped appropriately. 4. **Signal Multiplexing:** Switching UART, SPI, or I2C lines between multiple controllers.