74LS189 64 Bit RAM
The 74LS189, also labeled as 74189 or 74HC189 in CMOS form, is a TTL logic static RAM IC offering 64 bits of storage organized into 16 words of 4 bits each. Designed for high-speed operation, it features buffered, diode-clamped address inputs to reduce loading on preceding stages and internal address decoding for efficient memory access.
Outputs are inverted and support tri-state operation, allowing easy integration into shared bus systems. Data is written when Chip Select (CS) is LOW and Write Enable (WE) is LOW; reading occurs when CS is LOW and WE is HIGH. When CS is HIGH, the outputs go into high-impedance mode.
This IC is widely used in retro computers, microprocessor trainers, and digital logic projects that require compact, fast, and reliable static RAM. It is also an excellent educational component for demonstrating memory architecture in TTL systems.
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⚙️ Technical Specifications
| Specification | Details |
|---|---|
| Memory Organization | 16 × 4 bits (64 bits total) |
| Output Type | Inverted, tri-state |
| Input Type | Buffered, diode-clamped |
| Logic Family | 74LS / 74HC / 74F |
| Operating Voltage | 4.75V – 5.25V |
| Package | DIP-16 |
| Access Time | ~25 ns (typical for 74LS series) |
| Operating Temperature | 0°C to +70°C |
| Control Inputs | CS (Chip Select), WE (Write Enable) |
💡 Use Cases & Applications
💻 Retro computing memory modules
📟 TTL-based microprocessor trainers
📊 Data buffering and register staging
🔬 Educational logic experiments
🖥️ Bus-shared memory in small-scale systems
⚠️ Precautions
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Outputs are inverted—design circuits accordingly.
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Avoid leaving control lines floating; tie unused inputs HIGH or LOW.
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Observe correct CS and WE logic to prevent accidental overwrites.
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Handle with ESD precautions; TTL inputs are static-sensitive.
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Do not exceed rated voltage or temperature limits.
🛠️ Related Products & Internal Links
🛒 Summary
The 74LS189 / 74189 / 74HC189 is a compact and fast TTL static RAM IC ideal for small-scale memory needs in digital logic systems. Its tri-state inverted outputs and robust TTL compatibility make it a reliable choice for embedded projects, retro computing, and educational labs.
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