SN74LS181 Arithmetic Logic Unit (ALU) and Function Generator – 4-Bit High-Speed Logic 24-Pin DIP

The SN74LS181 is a legendary integrated circuit that serves as the "brain" or Arithmetic Logic Unit (ALU) for classic computer architectures. It is a bit-slice processor capable of performing a wide array of operations—from simple addition and subtraction to complex logic functions like AND, OR, NAND, and XOR—all within a single 24-pin package. By manipulating the four function-select inputs (S0 through S3), the user can program the chip to execute 32 different functions. In arithmetic mode, it handles operations like A plus B, A minus B, and even increment/decrement functions. In logic mode, it treats the inputs as independent bits, allowing for high-speed bitwise manipulation. Its ability to provide "look-ahead carry" makes it significantly faster than cascading simple adders. The 24-pin DIP package is a centerpiece for educational computer science projects, vintage computer restoration, and "homebrew" CPU designs. Whether you are building a discrete logic computer from scratch or studying the fundamentals of processor architecture, the SN74LS181 remains one of the most significant and educational components in digital electronics history.

Key Features:

Full Look-Ahead Carry Features internal carry look-ahead logic for high-speed arithmetic operations across all 4 bits.

Versatile Operation Modes Includes a Mode Control (M) pin to switch instantly between logic-only functions and full arithmetic operations.

Cascadable for Higher Word Lengths Designed with Ripple Carry and Look-Ahead Carry outputs to easily expand to 8, 16, or 32-bit processors.

Standard LS-TTL Technology Provides a reliable balance of high-speed switching and low power consumption for 5V systems.

Open-Collector A=B Output Includes a dedicated comparator output to indicate when two 4-bit inputs are equal.