Encoder: An encoder is a digital circuit that performs the inverse operation of a decoder. An encoder has a number of inputs, only one of which is activated at a given time, and produces an output code depending on which input is activated. That is, the outputs of an encoder generate the binary code corresponding to the input value. IC 74147 is a decimal-to-BCD encoder as shown below. Note that the inputs and outputs of the chip are Active-LOW, and it is a Priority encoder - the highest input has priority.
(a) Fill out the following priority encoder truth-table
Table 6.18 Truth table of 74147
Active-low decimal inputs 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 T 1 1 1 1
Active-low BCD outputs D c B 1 1 1 1 1 1 I 0 1 1 0 1
LSB A
1
2
1
1 1 0
B
BCD indino
0
Decimal input
MSB
X
X
X
X
X
X
X
0
1 0
0 0
1 1
1 1
1 0
b Connect each out X X X X and then to an LE 1, as shown below. Cvuuev ue pu v AIINTIINAAT1ADANTCAIIMTCML input at a time. Observe the LED and 7-segment display to see if the corresponding output is right.
Decoder 7447
74147