282
Digital Electronics
A
B
C
D 0
D 1
D 2
D 3
D 4
D 5
D 6
D 7
Figure 8.15 Octal-to-binary encoder.
Table 8.8 Truth table of an encoder.
D 0
D 1
D 2
D 3
D 4
D 5
D 6
D 7
A
B
C
1
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
1
0
0
0
0
1
0
0
0
0
0
1
1
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
1
0
0
1
0
1
0
0
0
0
0
0
1
0
1
1
0
0
0
0
0
0
0
0
1
1
1
1
encoder will then be modified to what is shown in Table 8.9. Looking at the last row of the
table, it implies that, if D 7 = 1, then, irrespective of the logic status of other inputs, the output is
111 as D 7 will only be encoded. As another example, Fig. 8.16 shows the logic symbol and truth
table of a 10-line decimal to four-line BCD encoder providing priority encoding for higher-order
digits, with digit 9 having the highest priority. In the functional table shown, the input line with
highest priority having a LOW on it is encoded irrespective of the logic status of the other input
lines.