SN74S257DE4

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The SN74S257DE4, which is categorized under Logic - Signal Switches, Multiplexers, Decoders, is a 4-bit multiplexer device. It is used to select data from multiple sources such as code converters, memory devices, and arithmetic logic units (ALUs). It enables one multiplexer to replace several multiplexers and combine four different input sources into one output. This structure significantly reduces hardware costs, space requirements, and system complexity.

Functions and applications

The SN74S257DE4 is a multiplexer that can select up to four 4-bit words and combine them into one output. It can multiplex 4-bit binarys, 2-bit Gray codes, and even 4-bit one-hot code with the same pinout. It includes two binary encoded select inputs (S0 and S1), two enable inputs (E1 and E2), and a common input and output bus (I/O bus). When E1 and E2 are both active, the SN74S257DE4 multiplexer is enabled and the output is set to the value of the selected input. E1 and E2 can often be combined into one enable input to reduce both cost and complexity.

The SN74S257DE4 is used in many applications such as data multiplexing and demultiplexing, code converters, digital signal processings (DSPs), arithmetic logic unit (ALU) operations, and transistor–transistor logic (TTL) decoding. Its ability to select 4-bit words makes it particularly useful in the operation of electronic calculators, shift registers and peripheral interfaces.

Working principle

The working principle of the SN74S257DE4 multiplexer is based on a combination of logic circuits and binary logic. Two binary encoded inputs, S0 and S1, serve as select inputs and are used to choose a specific word. The input word is selected according to the binary combination of S0 and S1—i.e., a different word is selected for each different binary combination of S0 and S1, allowing up to four words to be selected from one multiplexer. When E1 and E2 are both active, the selected word is directed to the output bus.

The SN74S257DE4 multiplexer operates with a simple yet effective internal circuit which employs Diode-OR (a logical structure consisting of diodes and OR logic gates) to eliminate the need for additional select logic. The signal must pass through either two or three selected diodes depending on the input signal code, thus avoiding the complexities of traditional multiplexers. This allows the multiplexer to select words based on the binary combination of S0 and S1, ensuring a fast and reliable selection.

Conclusion

The SN74S257DE4 multiplexer is a powerful and reliable 4-bit multiplexer device that can combine four different input sources into one output. Its ability to select 4-bit words make it a great choice for applications such as data multiplexing and demultiplexing, code converters, DSPs, ALU operations, and TTL decoding. Its internal circuit employs Diode-OR structures, eliminating the need for additional select logic and allowing for fast and reliable selection.

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