CD74AC139E

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CD74AC139E is a high speed CMOS decode dual 1-of-8 decoder designed to prioritize three binary address inputs A0, A1 and A2 with active low outputs. Unlike most decoders, it utilizes a non-inverting 3-state output capability. This feature allows multiple decoders to be connected together, in a manner that provides priority decoding capabilities.

As a logic-signal switch, the CD74AC139E is used to translate a 3-bit binary input signal into one of eight output signals. This is done by decoding the binary address in a manner that selects one of the outputs, based on the input signals. The other seven outputs will remain in their high impedance state.

In its operation, the circuit design of the CD74AC139E utilizes a three-input NOR gate for each of its functions. These NOR gates have 2 inputs and an output that is fed back to the first input. The NOR gates are connected together to form a three input decoder, with the binary inputs connected to the first input of each NOR gate, and the other seven outputs connected to corresponding inputs of each NOR gate.

When a particular binary address is inputted into the CD74AC139E, one of the inputs from the three-input NOR gate is activated. This activated input produces a high voltage on the output of the NOR gate, which is then fed back to the first input of the NOR gate. This in turn causes the output of the NOR gate to be activated and the associated output to be set to active low.

In addition to basic decoding functions, the CD74AC139E has several other common applications. These include:

• Multiplexer - When multiplexing with the CD74AC139E, the three binary address inputs are used to control which of the eight outputs is active or inactive at any one time. Multiplexers offer superior speed and flexibility compared to regular static switches.
• Encoder - When used as an encoder, the eight outputs become address lines that can coordinate with eight data inputs. Each data input is encoded with a particular binary address, allowing the device to convert data into serially encoded signals.
• Parallel to Serial Data Conversion - The CD74AC139E is used to convert parallel data to serial data by sequentially activating the eight output lines one-by-one, based on the binary inputs. This allows for the transmission of data over longer distances.

Overall, the CD74AC139E is a reliable and versatile logic device that can be used for basic decoding, multiplexing and encoder applications. It is a fast and efficient device which, when combined with its 3-state output capability, can be used for a variety of tasks.

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