Encoders and Decoders

Content to be covered: Encoders Decoders Example of using decoders with MUX Conclusion

ENCODERS An encoder is a device that is used to convert a signal or certain data into code. This kind of conversion is done for a variety of reasons, the most common being data compression. Other reasons for using encoders include: data encryption for making the data secure translating data from one code to another new or existing code.

ENCODERS Encoders may be analog or digital devices. In analog devices, the encoding is done using analog circuitry While in digital encoders the encoding is done using program algorithms

ENCODERS vs MULTIPLEXORS An encoder refers to a device that is used to change a signal or data into a code. Whereas A Multiplexer or mux is a device which performs multiplexing or it takes information from more than one channels and outputs into a single channel.

Example of an ENCODER Inputs Output

Activity Draw: 2 input encoder 4 input encoder 16 input encoder

Further example of Encoders If in an encoder the following input was given, the output/address would be as indicated: A B C D E F G H S0 S1 S2 1 0 0 0 0 0 0 0 0 0 0

Further example of Encoders 1 If in an encoder the following input was given, the output/address would be as indicated: A B C D E F G H S0 S1 S2 0 0 0 0 0 1 0 0 1 0 1

Content to be covered: Encoders Decoders Example of using decoders with MUX Conclusion

DECODERS A decoder, on the other hand, functions the reverse of an encoder. It is a device that is used to decode an encoded signal or data. It does this to help retrieve the data that was encoded in the first place. Both encoders and decoders usually function in cycle, i.e., an application that uses an encoder would ideally also require a decoder.

DECODERS A decoder chooses one of the wires and make it output 1. The output whose index is given by the binary value on S (select input) is set to 1. All others are set to 0. Only one wire can be ‘ON’ at a time.   Whichever one is ‘ON’ is based on the input (ie @ the selector).

Example of a DECODER Output NB: Only ONE of the line will have the value 1; others will have 0.

Activity Draw: 1 input decoder 2 input decoder 4 input decoder

Further example of Decoders If in a decoder the following selects were made, the output would be as indicated: S0 S1 S2 A B C D E F G H 1 0 1 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0

Further example of Decoders If in a decoder the following selects were made, the output would be as indicated: S0 S1 S2 A B C D E F G H 0 1 0 0 0 1 0 0 0 0 0

Content to be covered: Encoders Decoders Example of using decoders with MUX Conclusion

Example of using decoders with MUX

Example of using decoders with MUX The decoder selected 01, which allows 01 to be set to 1, hence allowing it to light up. The MUX gets its input from the wire that has been lit-up by the decoder.

Example of using decoders with MUX The input to the MUX of 1 or 0 is based on if the lines are connected (1) or disconnected (2). In the example given above, if the select for the 2-1 MUX is 00, the output would be 0.

Example of using decoders with MUX Please Note: You don’t always have equal rows and columns. A decoder does not have an output line, and the input (which is to the side) is the select lines.

Activity Draw: 2-4 Decoder with a 8-1 bit Mux (using only 2-1 bit muxes) LOL

Content to be covered: Encoders Decoders Example of using decoders with MUX Conclusion

Conclusion If the encoders are the opposite of decoders, then that means that the outputs and inputs of the decoder are swapped.  That means that what would normally be the select lines on the decoder (which are inputs) would now be the outputs of the encoder.  Its purpose would be to produce the binary encoding of the index whose input is high.

Conclusion That is, the encoder will have 2n inputs and n outputs, and only one of the inputs is expected to be high at any one moment.  Encoders are useful for components like content-addressable memory, where you put in the data you want, and the address where it is stored is returned as a result.

The END