74251 8-Inputs Data Selector/Multiplexer IC

74251 8-Inputs Data Selector/Multiplexer IC – Product Overview

The 74251 is a high-performance 8-input data selector and multiplexer IC. Designed for fast, reliable digital data routing, this TTL-based 8-to-1 multiplexer selects one of eight inputs and presents it on a single output line according to the 3-bit select inputs. It provides both true and complemented outputs and includes an enable input that places the outputs in a high-impedance state when disabled. The device is ideal for combinational and sequential logic systems, memory decoding and general data selection in control and communication systems.

Key Features

• 8-to-1 multiplexer with tri-state output control
• Three selection lines (S2, S1, S0) to select one of D0 to D7
• True output (Y) and complemented output (W) for flexible logic design
• Active enable input (G) that forces outputs to high-impedance when HIGH
• Built on TTL technology for fast switching and high noise immunity
• Standard 24-pin Dual Inline Package (DIP) for breadboard and PCB use
• Low power consumption with ±8 mA output drive and typical 20 ns propagation delay

Functional Description

• When the enable input G is LOW, the selected data input (D0 to D7) is routed to the true output Y and the complemented version appears at W.
• The selection inputs S2, S1 and S0 form a 3-bit binary code to choose which of the eight inputs is transmitted to the outputs.
• When the enable input G is HIGH, both outputs are placed in a high-impedance (Hi-Z) state, allowing bus sharing and tri-state bus control.
• TTL-level input thresholds: VIH >= 2.0 V and VIL <= 0.8 V, supply voltage 4.75 V to 5.25 V.

Applications

• Digital signal multiplexing and data routing
• Logic function generation and combinational logic circuits
• Memory address decoding and selection
• Data selection in microcontroller and processor interfaces
• Arithmetic logic units (ALUs) and arithmetic data paths
• Communication and switching systems requiring fast selection

Specifications

• Type: 8-to-1 data selector/multiplexer
• Logic family: TTL (Transistor-Transistor Logic)
• Supply voltage (VCC): 4.75 V to 5.25 V
• Input high voltage (VIH): >= 2.0 V
• Input low voltage (VIL): <= 0.8 V
• Output current: +/- 8 mA
• Propagation delay (typical): 20 ns
• Operating temperature range: 0 C to +70 C
• Package type: 24-pin Dual Inline Package (DIP)

Typical Use and Design Tips

• Use the tri-state enable (G) to share a data bus among multiple devices. Drive G HIGH to disconnect outputs from the bus.
• When interfacing to CMOS logic, ensure proper TTL to CMOS level translation where required, especially for inputs near threshold levels.
• By using both Y and W outputs, designers can avoid extra inverters in systems that need both true and complemented signals.
• Place decoupling capacitors close to the VCC and GND pins to improve noise immunity and switching stability.
• For prototyping, the 24-pin DIP fits standard breadboards for quick test setups and signal validation.

Ordering and Packaging

The 74251 is commonly supplied in a 24-pin DIP that is suitable for breadboards and through-hole PCBs. Contact your distributor for availability, lead times and packaging alternatives such as surface mount versions from compatible logic families.

Note: Images are for illustration purposes only.