The **74HE373C** (often referred to as the **74HC373** in standard High-speed CMOS series) is a popular electronic component used in digital circuits. It is an **Octal Transparent D-Type Latch** with 3-state outputs. --- ## 1. Core Technical Specifications The "HE" or "HC" designation indicates it belongs to the High-speed CMOS family, which combines the low power consumption of CMOS with the speed of TTL. | Feature | Specification | | :--- | :--- | | **Number of Latches** | 8 (Octal) | | **Logic Type** | Transparent D-Type Latch | | **Supply Voltage (Vcc)** | 2.0V to 6.0V | | **Output Type** | 3-State (High, Low, High-Impedance) | | **Propagation Delay** | ~12ns to 30ns (depending on voltage) | | **Drive Capability** | Can drive up to 15 LSTTL loads | --- ## 2. Pin Configuration and Functions The device usually comes in a 20-pin package (DIP, SOIC, or TSSOP). ### Key Pins: * **D0 - D7 (Inputs):** The eight data input lines. * **Q0 - Q7 (Outputs):** The eight data output lines. * **LE (Latch Enable):** Controls the "transparency" of the device. * **OE (Output Enable):** Controls whether the outputs are active or in a high-impedance (disconnected) state. --- ## 3. How It Works (Truth Table) The device operates based on the state of the **Latch Enable (LE)** and **Output Enable (OE)** pins. | OE | LE | D | Q (Output) | Mode | | :--- | :--- | :--- | :--- | :--- | | L | H | L | L | Transparent (Follows Input) | | L | H | H | H | Transparent (Follows Input) | | L | L | X | Q0 | Latched (Holds previous value) | | H | X | X | Z | High-Impedance (Disconnected) | * **Transparent Mode:** When LE is HIGH, the outputs follow the inputs directly. * **Latched Mode:** When LE goes LOW, the data present at the inputs at that moment is "frozen" or latched. Changes to D no longer affect Q. * **3-State Output:** When OE is HIGH, the outputs are effectively disconnected (High-Z), allowing multiple devices to share a single data bus. --- ## 4. Common Applications 1. **Address Latching:** Used in microcontroller circuits (like the 8051) to separate the multiplexed Address and Data buses. 2. **Buffer/Driver:** Acts as a high-current driver for LEDs or other components. 3. **Data Storage:** Temporary 8-bit storage for bus-oriented systems. 4. **I/O Expansion:** Expanding the number of output ports on a CPU.