Encoder

The Encoder IC can be viewed as a device which produce or generate the binary code for a particular input. In this example, the 10 input pins are connected to a keypad consisting of 10 keys '0' to '9'. When the key '9' is depressed, the particular input signal is active low, and hence the generated output code is binary "1001", representing the decimal number 9.

Now, for encoder (as different from the decoder), there is a possibility of multiple inputs active at the same time. For the example given above, this happens when two or more keys are depressed at the same time. Hence, there must be a priority scheme to give higher priorities to some inputs. For this case, if another key lower value than '9' is depressed at the same time, the priority will be given to '9' and the output will remain at "1001".

Hence, the truth table for the encoder is:




[more: timing diagram]