## Overview of the 74ACT16640 The **74ACT16640** is a high-performance CMOS 16-bit bus transceiver. It is primarily used for asynchronous two-way communication between data buses. This component belongs to the "ACT" family, meaning it uses Advanced CMOS technology and has TTL-compatible inputs. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Logic Family** | ACT (Advanced CMOS, TTL Input Compatible) | | **Bit Width** | 16-Bit (organized as two 8-bit sections) | | **Output Type** | 3-State (Inverting) | | **Supply Voltage ($V_{CC}$)** | 4.5V to 5.5V | | **Propagation Delay** | ~5.0 ns (Typical) | | **Output Current ($I_{OH}/I_{OL}$)** | -24mA / 24mA | | **Operating Temperature** | -40°C to +85°C | --- ### 2. Pin Functions and Logic Operation The device is divided into two 8-bit transceivers. The direction of data flow and the output state are controlled by the **Direction (DIR)** and **Output Enable ($\overline{OE}$)** pins. #### Control Logic Table | $\overline{OE}$ | DIR | Operation | | :---: | :---: | :--- | | L | L | B data to A bus (Inverted) | | L | H | A data to B bus (Inverted) | | H | X | Isolation (High-Z State) | * **$\overline{OE}$ (Output Enable):** When High, the device enters a high-impedance state, effectively disconnecting the buses. * **DIR (Direction Control):** Determines whether data flows from A to B or B to A. * **Inverting Logic:** This specific model (**16640**) provides inverted outputs (e.g., if Input A is High, Output B will be Low). --- ### 3. Electronic Characteristics #### A. TTL Compatibility The "ACT" designation indicates that the input thresholds are compatible with standard TTL (Transistor-Transistor Logic) levels. This allows the chip to interface between older bipolar logic and modern CMOS systems without needing level shifters. #### B. 3-State Outputs The 3-state (Tri-state) outputs allow multiple devices to be connected to the same bus lines. Only one device drives the bus at a time, while others remain in a high-impedance state to prevent data collisions. #### C. Power Dissipation Being a CMOS device, it features very low static power consumption. However, power consumption increases with frequency due to the charging and discharging of internal and load capacitances. --- ### 4. Common Applications * **Bus Buffering:** Strengthening signals for driving long PCB traces or backplanes. * **System Isolation:** Disconnecting subsystems from the main CPU bus to reduce loading. * **Data Inversion:** Used in systems where active-low logic is required from an active-high source. --- ### 5. Package Example (Typical) The 74ACT16640 is commonly found in high-pin-count surface mount packages to accommodate the 16-bit width: ```text SSOP: Shrink Small-Outline Package TSSOP: Thin Shrink Small-Outline Package ```