The GD74LS138 is a 3-to-8 line decoder/demultiplexer from the 74LS series of logic gates. It accepts three binary address inputs (A, B, and C) and activates one of eight output lines (Y0 through Y7) based on the binary value of the address inputs. It also has three enable inputs (G1, /G2A, /G2B) which must be at their appropriate logic levels for the device to be enabled and the selected output to go low. The outputs are active-low, meaning the selected output line will be low (logic 0) while all other outputs remain high (logic 1).
Applications
- Memory address decoding
- Data routing and selection
- Output enabling for multiple devices
- Chip selection in memory systems
- Control logic for peripherals
Features
- 3-to-8 line decoding/demultiplexing
- Active-low outputs
- Three enable inputs for flexible control
- Low-Power Schottky TTL circuitry
- Typical propagation delay of 21 ns
- Low power consumption
Benefits
- Simplifies address decoding in memory systems
- Reduces component count by providing a single chip solution
- Enables flexible control of multiple devices
- Offers good speed performance for a variety of applications
- Minimizes power consumption
- Easy to interface with other TTL devices
Additional Details
The GD74LS138 typically comes in a 16-pin DIP (Dual In-line Package). It is crucial to consult the datasheet for specific electrical characteristics, timing diagrams, and pinout information. The enable inputs provide a means to cascade multiple '138 decoders to create larger decoding arrays. For example, two '138s can be used to create a 4-to-16 line decoder. The operating temperature range is typically 0°C to 70°C.
The device's active-low outputs are useful for directly driving LEDs or other devices that require a low-level signal to be activated. The 'LS' designation indicates that the device utilizes Schottky diodes to prevent saturation of the transistors, which improves switching speed. This makes the GD74LS138 suitable for applications where faster address decoding or data routing is needed.
