The **U74HCT640G-R20-R** is an integrated circuit (IC) belonging to the 74HCT family. It is specifically an **Octal Bus Transceiver with 3-State Inverting Outputs**. It is commonly used for asynchronous two-way communication between data buses. --- ### 1. General Specifications | Parameter | Value / Description | | :--- | :--- | | **Logic Family** | HCT (High-speed CMOS with TTL-compatible inputs) | | **Function** | Octal Bus Transceiver (Inverting) | | **Output Type** | 3-State (High, Low, High-Impedance) | | **Number of Channels** | 8-bit | | **Supply Voltage ($V_{CC}$)** | 4.5V to 5.5V | | **Operating Temperature** | -40°C to +85°C | --- ### 2. Key Features and Pins The device features 8 pairs of data lines and two control pins that determine the direction and state of the data flow. * **Inverting Logic:** Unlike the 74HCT245, the 640 series **inverts** the data. If a "High" is sent to the input, a "Low" is received at the output. * **Direction Control (DIR):** * **High:** Data flows from A to B. * **Low:** Data flows from B to A. * **Output Enable ($\overline{OE}$):** * **Low:** Device is active. * **High:** Outputs are in a high-impedance (High-Z) state, effectively disconnecting from the bus. --- ### 3. Logic Truth Table The following table describes how the control signals affect the data flow: | $\overline{OE}$ | DIR | Operation | | :---: | :---: | :--- | | L | L | B data to A bus (Inverted) | | L | H | A data to B bus (Inverted) | | H | X | Isolation (High-Z) | --- ### 4. Technical Applications * **Bus Buffering:** Used to drive high-capacitance loads or multiple devices on a single data bus. * **Voltage Level Shifting:** Because it is "HCT," it can interface between 3.3V/5V TTL logic levels and CMOS circuits. * **Isolation:** The 3-state outputs allow multiple transceivers to share the same bus without interference when disabled. --- ### 5. Part Number Breakdown * **U74:** Manufacturer specific prefix (Unisonic Technologies / UTC). * **HCT:** High-speed CMOS with TTL threshold levels. * **640:** Functional code for Octal Inverting Transceiver. * **G:** Usually denotes Green/Halogen-free packaging. * **R20/R:** Refers to the specific package type (e.g., SOP-20 or TSSOP-20) and Taping/Reel delivery format.