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7400 Series Guide: 74HC139/74LS139 (2-to-4 decoder)

The 74×139 (ex 74HC139) is a chip that contains two independent 2-to-4 line decoders/demultiplexers.

In this guide, you’ll learn the things you need to know about this chip in order to effectively use decoders and demultiplexers in your own projects.

74HC139 / 74LS139 Package And Pinout

What does the 74HC139 / 74LS139 do?

The 74×139 is a dual 2-to-4 line decoder/demultiplexer. This chip has two independent sections that can each take two binary inputs and turn them into four separate outputs.

Here’s how it works:

  • Each section has two data inputs (let’s call them A and B) and four outputs (Y0 to Y3).
  • Depending on the combination of A and B, one of the four outputs will be driven LOW, while the others remain HIGH.
  • There is also an enable input for each section. The outputs are all HIGH if the enable input is not active.

This chip is useful when you want to select one of several signals or routes using binary signals, like in memory address decoding in computers.

How To Use This Chip

The 74HC139 comes in a 16-pin package, and you need to connect it to power before you can use it. Most 7400 ICs support a VCC voltage of 5V. One difference between the HC and LS version of the chip is that the 74HC139 supports 2V to 6V, while the 74LS139 only supports 5V.

74HC chips can normally supply a maximum of 4 mA from an output pin. If you’re using the 74LS version, the maximum current you can pull out of one output pin is 0.4 mA when the pin is high (sourcing) or 8 mA when the pin is low (sinking).

But these values can differ between models, so check the datasheet of your model to verify.

Once you’ve connected it to power, you can use the Demultiplexer/decoder inside.

7400 series IC connected to 5V on a breadboard
The 74HC139/74LS139 IC connected to power

74×139 Pinout

The 74×139 has 16 pins and contains two 1-of-4 inverting decoder/demultiplexer laid out as shown in the pinout diagram below:

74139 Pinout
Pin NamePin #TypeDescription
1EN1InputEnable input for the first demultiplexer/decoder (active low).
1S02InputSelector input bit 0 for the first demultiplexer/decoder.
1S13InputSelector input bit 1 for the first demultiplexer/decoder.
1Y04OutputInverted output bit 0 from the first demultiplexer/decoder.
1Y15OutputInverted output bit 1 from the first demultiplexer/decoder.
1Y26OutputInverted output bit 2 from the first demultiplexer/decoder.
1Y37OutputInverted output bit 3 from the first demultiplexer/decoder.
GND8PowerConnect to ground (GND).
2Y39OutputInverted output bit 3 from the second demultiplexer/decoder.
2Y210OutputInverted output bit 2 from the second demultiplexer/decoder.
2Y111OutputInverted output bit 1 from the second demultiplexer/decoder.
2Y012OutputInverted output bit 0 from the second demultiplexer/decoder.
2S113InputSelector input bit 1 for the second demultiplexer/decoder.
2S014InputSelector input bit 0 for the second demultiplexer/decoder.
2EN15InputEnable input for the second demultiplexer/decoder (active low).
VCC16PowerPositive power supply. Connect to +5V power.
Pin overview for the 74×139 IC

Alternatives and Equivalents for 74HC139 / 74LS139

There are many versions of the 74×139 chip. They all have the same functionality, but with different specifications such as supported voltages and maximum current output.

Here’s a list of a few equivalents of this chip:

  • 74HC139 (High-speed CMOS)
  • 74HCT139 (High-speed CMOS, TTL compatible)
  • 74LS139 (High-speed TTL)
  • 74LVC139 (Low Voltage TTL)
  • 74AC139 (Advanced CMOS)
  • 74ALS139 (Advanced Low-Power Schottky TTL)
  • 74F139 (Very High Speed)
  • 74C139 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74HC139 and SN74LS139 by Texas Instruments.

Can’t find the 74×139 anywhere? Then try one of the following IC alternatives:

  • 74×137 – Dual 2-to-4 line decoder/demultiplexer.
  • 74×138 – 3-to-8 line decoder/demultiplexer.
  • 74×237 – Dual 2-to-4 line decoder/demultiplexer with address latches.
  • CD4555 – Dual 1-of-4 line decoder/demultiplexer.
  • CD4556 – Dual 1-of-4 line decoder with address latch.

If you can’t find the 74×139 IC in your local electronics store, don’t worry, you’ll most likely find it in one of the stores listed on this page of online stores where you’ll find components and tools for all your electronics projects.

Datasheet for the 74LS139 and 74HC139 chips

Download the PDF datasheet for your version of the 74×139 here:

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