74ls157 sn74ls157n dip ic

🔹 74LS157 / SN74LS157N – Quad 2-Input Multiplexer (DIP-16)

A TTL logic integrated circuit containing four independent 2-input multiplexers (data selectors) in a single 16-pin package. It selects one of two 4-bit data sources and routes it to its four outputs based on a common select line, making it useful for data routing, bus switching, and function selection in digital systems.

✅ Specifications:

• Part Number: 74LS157, SN74LS157N (DIP package)

• Type: Quad 2-Input Multiplexer (Data Selector)

• Logic Family: TTL (Low-Power Schottky)

• Supply Voltage (Vcc): 5V ±5% (4.75V to 5.25V)

• Number of Circuits: 4 independent multiplexers

• Inputs per Mux: 2 data inputs (1A, 1B, etc.) + 1 common Select (S)

• Control Pins:

  • Select Input (S): Common to all four muxes. Chooses between input A or B.

  • Strobe / Enable (G̅): Active LOW. When HIGH, forces all outputs (Y) LOW.

• Truth Table (per mux):

  G̅ (Enable)	S (Select)	Output (Y)
  H (1)	X	L (0)
  L (0)	L (0)	A
  L (0)	H (1)	B

• Propagation Delay: ~15ns (typical)

• Output Current: Can source/sink up to 0.4mA / 8mA

• Package: DIP-16 (Dual In-Line, 16-pin, through-hole)

• Operating Temperature: 0°C to +70°C (Commercial)

⚙️ Key Features:

• Common Select Line: A single select pin controls all four multiplexers simultaneously.

• Active LOW Enable: Allows for easy output gating and bus interfacing.

• Non-Inverting Outputs: The selected input (A or B) appears at output Y unchanged.

• Wide Operating Voltage: Standard 5V TTL compatibility.

• Industry Standard: A classic, widely-available logic chip for data routing.

📦 Typical Applications:

• Data Source Selection: Switching between two 4-bit data buses (e.g., from two different sensors or registers).

• Arithmetic Logic Unit (ALU) Input Selection: Choosing operands in simple CPU designs.

• Bus Multiplexing: Sharing a common data path between two sources.

• Function Generators: Selecting between different logic functions or signal paths.

• Address Decoding Expansion: In memory-mapped I/O systems.

• Retro Computing & Education: Used in classic computer designs and for teaching digital logic concepts.

🔧 Pinout (DIP-16):

• Pin 1: Select Input (S) – Common selection for all muxes.

• Pin 2: 1A – Data input A for Mux 1.

• Pin 3: 1B – Data input B for Mux 1.

• Pin 4: 1Y – Output for Mux 1.

• Pin 5: 2A – Data input A for Mux 2.

• Pin 6: 2B – Data input B for Mux 2.

• Pin 7: 2Y – Output for Mux 2.

• Pin 8: GND

• Pin 9: 3Y – Output for Mux 3.

• Pin 10: 3B – Data input B for Mux 3.

• Pin 11: 3A – Data input A for Mux 3.

• Pin 12: 4Y – Output for Mux 4.

• Pin 13: 4B – Data input B for Mux 4.

• Pin 14: 4A – Data input A for Mux 4.

• Pin 15: Strobe / Enable (G̅) – Active LOW.

• Pin 16: VCC (+5V)

⚠️ Important Design Notes:

• TTL Logic Levels: Input HIGH: min 2.0V, Input LOW: max 0.8V. Not 5V CMOS compatible without pull-ups.

• Unused Inputs: Do not leave TTL inputs floating. Tie unused data inputs (A, B) to GND or VCC through a resistor.

• Power Supply Decoupling: Always use a 0.1µF ceramic capacitor between VCC (pin 16) and GND (pin 8), placed close to the IC.

• Output Loading: Do not exceed the fan-out limits. For driving many inputs, use a buffer (e.g., 74LS244).

• Alternate Part: The 74LS158 is identical but has inverting outputs.