Use 4 variable K-maps for getting simplified expressions for each output. The Truth table of 4 to 2 priority encoder is shown below. In this case, the output, V will be equal to 0. If all the inputs of encoder are ‘0’, then the code available at outputs is not a valid one. In this case, the output, V will be equal to 1. If at least one input of the encoder is ‘1’, then the code available at outputs is a valid one. We considered one more output, V in order to know, whether the code available at outputs is valid or not. In this case, even if more than one input is ‘1’ at the same time, the output will be the (binary) code corresponding to the input, which is having higher priority. Here, the input, Y 3 has the highest priority, whereas the input, Y 0 has the lowest priority. Priority EncoderĪ 4 to 2 priority encoder has four inputs Y 3, Y 2, Y 1 & Y 0 and two outputs A 1 & A 0. This encoder is called as priority encoder. Then, the output of encoder will be the (binary) code corresponding to the active High input(s), which has higher priority. So, to overcome these difficulties, we should assign priorities to each input of encoder. This is neither equivalent code corresponding to Y 3, when it is ‘1’ nor the equivalent code corresponding to Y 6, when it is ‘1’. For example, if both Y 3 and Y 6 are ‘1’, then the encoder produces 111 at the output. If more than one input is active High, then the encoder produces an output, which may not be the correct code. Because, it could be the code corresponding to the inputs, when only least significant input is one or when all inputs are zero. There is an ambiguity, when all outputs of encoder are equal to zero. Drawbacks of Encoderįollowing are the drawbacks of normal encoder. These OR gates encode the eight inputs with three bits. The above circuit diagram contains three 4-input OR gates. The circuit diagram of octal to binary encoder is shown in the following figure. We can implement the above Boolean functions by using four input OR gates. The Truth table of octal to binary encoder is shown below. The block diagram of octal to binary Encoder is shown in the following figure.Īt any time, only one of these eight inputs can be ‘1’ in order to get the respective binary code. Octal to binary encoder is nothing but 8 to 3 encoder. Octal to binary Encoder has eight inputs, Y 7 to Y 0 and three outputs A 2, A 1 & A 0. These OR gates encode the four inputs with two bits Octal to Binary Encoder The above circuit diagram contains two OR gates. The circuit diagram of 4 to 2 encoder is shown in the following figure. We can implement the above two Boolean functions by using two input OR gates. Inputsįrom Truth table, we can write the Boolean functions for each output as The Truth table of 4 to 2 encoder is shown below. The block diagram of 4 to 2 Encoder is shown in the following figure.Īt any time, only one of these 4 inputs can be ‘1’ in order to get the respective binary code at the output. Let 4 to 2 Encoder has four inputs Y 3, Y 2, Y 1 & Y 0 and two outputs A 1 & A 0. It is optional to represent the enable signal in encoders. Therefore, the encoder encodes 2 n input lines with ‘n’ bits. It will produce a binary code equivalent to the input, which is active High. It has maximum of 2 n input lines and ‘n’ output lines. An Encoder is a combinational circuit that performs the reverse operation of Decoder.
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