2:4 Decoder DeMux 74139

The 2:4 Decoder DeMux 74139 is a 74-series logic IC that contains two independent 2-to-4 line decoders/demultiplexers in one 16-pin package. Each decoder takes a 2-bit binary input and pulls exactly one of its four outputs LOW, as long as its enable input is LOW. It is widely used for address decoding, selecting one of four devices and digital logic lab work.

2:4 Decoder DeMux 74139 Specifications

• Function: 2 × 2-to-4 line decoder/demultiplexer
• Inputs per decoder: A and B (select), /G (enable, active LOW)
• Outputs per decoder: Y0 to Y3, active LOW
• Truth table: /G = 1 → all outputs HIGH; /G = 0 → BA = 00 selects Y0, 01 Y1, 10 Y2, 11 Y3
• Supply voltage: 5 V
• Package: 16-pin DIP
• Pinout: 1 /1G, 2 1A, 3 1B, 4–7 1Y0–1Y3, 8 GND, 9–12 2Y3–2Y0, 13 2B, 14 2A, 15 /2G, 16 VCC

2:4 Decoder DeMux 74139 Applications

• Address decoding for memory and I/O chips
• Selecting one of four LEDs, displays or devices
• Demultiplexing one data line to four outputs, using /G as the data input
• Controlling four lines from two microcontroller pins
• Digital logic labs and university electronics courses

What's in the Box

• 1 × 74139 dual 2-to-4 decoder IC

Tip: The outputs are active LOW, so the selected output goes to 0 V: to light an LED on the selected line, connect it from VCC through a resistor to the output. Place a 100 nF capacitor between pins 16 and 8 and tie unused inputs to VCC or GND.

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