The **SN74LS393D** is a high-speed CMOS/TTL compatible integrated circuit featuring two independent 4-bit binary counters. It is widely used in digital electronics for frequency division, timing, and counting applications. --- ## 1. Core Technical Specifications The "LS" in the part number signifies **Low-power Schottky** technology, which balances high speed with moderate power consumption. | Parameter | Specification | | :--- | :--- | | **Logic Family** | LS-TTL | | **Function** | Dual 4-Bit Binary Counter | | **Supply Voltage ($V_{CC}$)** | 4.75V to 5.25V | | **Max Clock Frequency** | 35 MHz (Typical) | | **Output Current** | 8 mA (High/Low) | | **Package Type** | SOIC-14 (Surface Mount) | | **Operating Temp** | 0°C to 70°C | --- ## 2. Internal Architecture & Logic The chip consists of two identical, independent 4-stage ripple counters. ### Pinout Configuration 1. **Clock Inputs ($1\bar{A}, 2\bar{A}$):** Negative-edge triggered. The counter increments when the clock signal transitions from High to Low. 2. **Clear Inputs ($1CLR, 2CLR$):** Active-High. Applying a high signal to these pins resets all four bits of the respective counter to zero ($Q_A$ through $Q_D = 0$). 3. **Outputs ($Q_A, Q_B, Q_C, Q_D$):** These represent the 4-bit binary value ($2^0, 2^1, 2^2, 2^3$). ### Counter Truth Table (Single Section) | Reset (CLR) | Clock ($\bar{A}$) | Output State | | :--- | :--- | :--- | | High (H) | X | All Outputs Low (0000) | | Low (L) | $\downarrow$ | Increment Binary Count | | Low (L) | $\uparrow$ | No Change | --- ## 3. Key Electronic Characteristics ### Ripple Counter Nature This is a **Ripple Counter**, meaning the clock signal only triggers the first flip-flop ($Q_A$). The output of $Q_A$ then acts as the clock for $Q_B$, and so on. * **Pros:** Simple internal design and low power. * **Cons:** "Propagation Delay" accumulates as the signal ripples through the bits. This can cause momentary "glitches" in the binary output during transitions. ### Power Management The LS technology uses Schottky-clamped transistors to prevent saturation, allowing for faster switching times than standard 7400 series chips while drawing significantly less power than the original TTL designs. --- ## 4. Common Applications * **Frequency Dividers:** By using specific outputs, you can divide an input frequency by 2, 4, 8, or 16. * **Digital Clocks:** Used in the stages that count seconds, minutes, or hours. * **Time-Delay Circuits:** Generating specific pulses after a set number of clock cycles. * **Address Generators:** Sequencing through memory addresses in simple computing systems.