Illustrate how 74147 series TTL can be used as a decimal-to-BCD encoder.
Ans. Available IC in 74 series is 74147 that is a priority encoder. Such IC has active low inputs and outputs. The significance of the word priority can be realized from the truth table. For example if 2 and 5 are low, the output will be consequent to 5 that has a higher priority than 2 that is the highest numbered input has priority over lower numbered inputs.
While an exact number is to be fed to the digital circuit in BCD code, then the switch consequent to which number is pressed.
Truth table of 74147
Active low decimal input's Active low BCD
74147 series TTL used as a decimal-to-BCD encoder