### M54HCT240 Overview The **M54HCT240** is a high-speed CMOS Octal Bus Buffer manufactured by STMicroelectronics. It features 3-state outputs and is designed specifically to be pin-compatible with standard low-power Schottky TTL (LSTTL) integrated circuits. --- ### 1. Key Technical Specifications | Parameter | Description | | :--- | :--- | | **Logic Family** | HCT (High-speed CMOS, TTL compatible) | | **Type** | Inverting Octal Buffer/Line Driver | | **Operating Voltage ($V_{CC}$)** | 4.5V to 5.5V | | **Input Threshold** | TTL Compatible ($V_{IH}$ min 2.0V) | | **Output Type** | 3-State (High Impedance mode supported) | | **Propagation Delay** | Approx. 13ns at 5V | | **Package Types** | DIP-20, SO-20, or LCCC-20 (Mil-grade) | --- ### 2. Functional Description The M54HCT240 contains **eight independent buffers** with inverting outputs. These are organized into two groups of four. * **Inverting Logic:** If the input is HIGH ($1$), the output is LOW ($0$), and vice versa. * **3-State Control:** Each group of four buffers is controlled by an Output Enable ($\overline{G}$) pin. * When $\overline{G}$ is **LOW**, the outputs are active. * When $\overline{G}$ is **HIGH**, the outputs enter a high-impedance state (effectively disconnected), allowing multiple devices to share the same bus lines. --- ### 3. Pin Configuration (DIP-20) | Pin No. | Symbol | Function | | :--- | :--- | :--- | | 1 | $1\overline{G}$ | Output Enable (Group 1) | | 2 to 9 | $1A_n / 2Y_n$ | Data Inputs / Inverting Outputs | | 10 | GND | Ground (0V) | | 11 to 19 | $2A_n / 1Y_n$ | Data Inputs / Inverting Outputs | | 20 | $V_{CC}$ | Supply Voltage | --- ### 4. Logic Truth Table For one buffer: | Input $A$ | Enable $\overline{G}$ | Output $Y$ | | :---: | :---: | :---: | | L | L | H | | H | L | L | | X | H | Z (High Impedance) | --- ### 5. Application Use-Cases * **Bus Driving:** Used to provide high current to drive heavily loaded backplanes or long cables. * **Memory Interfacing:** Acting as a bridge between a CPU and memory modules to manage data flow. * **Voltage Level Shifting:** Because it is HCT, it can interface 3.3V logic signals to 5V systems (provided $V_{CC}$ is 5V).