name the 7400 series ttl chip which is a priority

Question

Name the 7400 series TTL chip which is a priority encoder. Write its truth table. 

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.

Truth table of 74147

Active low decimal input's                                                           Active low BCD outputs
1	2	3	4	5	6	7	8	9	D	C	B	A
1	1	1	1	1	1	1	1	1	1	1	1	1
0	1	1	1	1	1	1	1	1	1	1	1	0
X	0	1	1	1	1	1	1	1	1	1	0	1
X	X	0	1	1	1	1	1	1	1	1	0	0
X	X	X	0	1	1	1	1	1	1	0	1	1
X	X	X	X	0	1	1	1	1	1	0	1	0
X	X	X	X	1	0	1	1	1	1	0	0	1
X	X	X	X	1	1	0	1	1	1	0	0	0
X	X	X	X	X	X	X	0	1	0	1	1	1
X	X	X	X	X	X	X	X	0	0	1	1	0