## Technical Overview of the MC74LS393D The **MC74LS393D** is a high-performance, low-power Schottky (LS) integrated circuit. It contains **two independent 4-bit binary counters** (74393 series) in a single 14-pin package. It is commonly used in digital circuits for frequency division, counting, and timing applications. --- ### 1. Key Internal Components and Logic The device consists of two separate 4-stage ripple counters. Each counter has: * **Four T-type Flip-Flops:** Internally connected to provide a divide-by-2, divide-by-4, divide-by-8, and divide-by-16 output. * **Clock Input ($\overline{CP}$):** Triggered on the **high-to-low (negative-edge)** transition of the clock pulse. * **Master Reset (MR):** An active-high input that clears all flip-flops simultaneously, forcing all outputs to a logical "0". --- ### 2. Pin Configuration The MC74LS393D is typically housed in a **SOIC-14** (Surface Mount) package. | Pin Number | Symbol | Description | | :--- | :--- | :--- | | 1 | 1$\overline{CP}$ | Clock Input Counter 1 (Active Falling Edge) | | 2 | 1MR | Master Reset Counter 1 (Active High) | | 3, 4, 5, 6 | 1Q0 - 1Q3 | Parallel Outputs Counter 1 (LSB to MSB) | | 7 | GND | Ground (0V) | | 8, 9, 10, 11| 2Q3 - 2Q0 | Parallel Outputs Counter 2 (MSB to LSB) | | 12 | 2MR | Master Reset Counter 2 (Active High) | | 13 | 2$\overline{CP}$ | Clock Input Counter 2 (Active Falling Edge) | | 14 | Vcc | Positive Supply Voltage (Typ. 5V) | --- ### 3. Electrical Specifications These parameters are standard for the "LS" (Low-power Schottky) TTL family. | Parameter | Symbol | Min | Typ | Max | Unit | | :--- | :--- | :--- | :--- | :--- | :--- | | Supply Voltage | $V_{CC}$ | 4.75 | 5.0 | 5.25 | V | | Input High Voltage | $V_{IH}$ | 2.0 | - | - | V | | Input Low Voltage | $V_{IL}$ | - | - | 0.8 | V | | Operating Frequency | $f_{max}$ | - | 32 | - | MHz | | Power Dissipation | $P_{D}$ | - | 50 | - | mW | --- ### 4. Functional Applications * **Frequency Division:** By taking the output from specific "Q" pins, the input clock frequency can be divided by powers of 2 (up to $2^8$ if both counters are cascaded). * **Digital Clocks:** Used as a stage for counting seconds, minutes, or hours. * **State Machines:** Providing the binary sequence required for sequential logic control. * **Binary Ripple Counting:** Because it is a ripple counter, the clock "ripples" through the flip-flops, meaning there is a slight propagation delay between the transitions of each bit. --- ### 5. Truth Table (Single Counter) | Master Reset (MR) | Clock ($\overline{CP}$) | Output State | | :--- | :--- | :--- | | H | X | All Outputs Low (L) | | L | $\downarrow$ | Count Up (Increment) | | L | $\uparrow$ | No Change |