CD74LS189 64-Bit Random Access Memory – 16 x 4 TTL Inverting 3-State RAM 16-Pin DIP

The CD74LS189 is a high-speed, 64-bit Random Access Memory (RAM) organized as 16 words of 4 bits each. It is a fundamental component for designers building hardware-level buffers, small register files, or look-up tables in discrete logic systems. Unlike modern high-density RAM, the 74LS189 provides direct, transparent access to memory cells via standard TTL logic levels. A unique feature of the 189 is its inverting 3-state outputs. When the Chip Select is active and the Write Enable is high, the data presented at the outputs is the inverse of what is stored in the addressed location. This chip is particularly valued in "homebrew" computer projects and educational digital trainers where students can observe the fundamental principles of memory addressing, data writing, and bus contention first-hand. The 16-pin DIP package is a classic through-hole format, making it easy to use on breadboards and reliable for long-term service in industrial control boards or vintage computing hardware. Whether you are building a custom micro-sequencer or repairing a 1980s-era arcade board, the CD74LS189 offers a robust and historically significant memory solution.

Key Features:

3-State Outputs Features high-impedance High-Z outputs that allow the chip to be connected directly to common data buses without conflict.

Inverting Data Outputs The data retrieved from the memory is the logical complement (inverted) of the data originally stored, a characteristic design of the 189 architecture.

Fast Access Time Utilizing Low Power Schottky technology to achieve typical access times of less than 35 nanoseconds, suitable for high-speed logic buffering.

Separate Read/Write Control Includes dedicated Write Enable (WE) and Chip Select (CS) inputs for precise control over data flow and memory protection.

Easy Expansion The 3-state outputs and Chip Select functionality allow multiple units to be combined to expand memory depth or width easily.