## 74ABT373CSC: Octal Transparent Latch with 3-State Outputs The **74ABT373CSC** is a high-performance integrated circuit (IC) belonging to the Advanced BiCMOS Technology (ABT) family. It consists of eight D-type latches with 3-state outputs, primarily used in bus-oriented systems and data buffering. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Logic Family** | ABT (Advanced BiCMOS) | | **Function** | Octal D-Type Transparent Latch | | **Output Type** | 3-State (Tri-state) | | **Operating Voltage ($V_{CC}$)** | 4.5V to 5.5V | | **Drive Capability** | IOL = 64mA; IOH = -32mA | | **Propagation Delay** | ~3.3ns (typical) | | **Package Type** | SOIC-20 (Small Outline Integrated Circuit) | --- ### 2. Functional Description The device features eight latches that appear "transparent" to the data when the Latch Enable (LE) input is high. #### Control Pins: 1. **Latch Enable (LE):** * **High (H):** The outputs ($Q_n$) follow the data inputs ($D_n$). This is the transparent mode. * **Low (L):** The data is latched. The outputs retain the state they had just before the LE transition from High to Low. 2. **Output Enable ($\overline{OE}$):** * **Low (L):** The outputs are active and represent the stored data. * **High (H):** The outputs are placed in a high-impedance state (Hi-Z), effectively disconnecting the device from the bus. --- ### 3. Truth Table | $\overline{OE}$ | LE | $D_n$ | $Q_n$ (Output) | Mode | | :---: | :---: | :---: | :---: | :--- | | L | H | H | H | Transparent | | L | H | L | L | Transparent | | L | L | X | $Q_0$ | Latched (Stable) | | H | X | X | Z | High Impedance | *Note: $Q_0$ = Level of output before LE transitioned to Low; Z = High Impedance.* --- ### 4. Hardware Implementation (Typical Wiring) Below is a conceptual representation of how to connect the 74ABT373 in a microcontroller circuit: ```c // Pseudo-code for controlling the Latch via GPIO void write_to_bus(uint8_t data) { SET_DATA_PINS(data); // Place data on D0-D7 SET_LE_HIGH(); // Latch becomes transparent DELAY_NS(5); // Meet setup time SET_LE_LOW(); // Data is now locked in SET_OE_LOW(); // Enable output to the system bus } ``` --- ### 5. Key Advantages of ABT Technology * **High Drive:** The 64mA sink current makes it ideal for driving heavily loaded backplanes or long bus lines. * **Low Power:** Uses CMOS inputs for low static power consumption while maintaining Bipolar speeds. * **Power-Up High Impedance:** The outputs remain in a high-impedance state during power-up/down, preventing bus contention or "glitching" on the system bus.