Page 53 - CITS - Electronic Mechanic - TT - 2024
P. 53
ELECTRONICS MECHANIC - CITS
Truth table for simple decade counter
Clock pulse Q3 Q2 Q1 Q0
0 0 0 0 0
1 0 0 0 1
2 0 0 1 0
3 0 0 1 1
4 0 1 0 0
5 0 1 0 1
6 0 1 1 1
7 0 1 1 1
8 1 0 0 0
9 1 0 0 1
10 0 0 0 0
Decade counter circuit diagram
We see from circuit diagram that we have used nand gate for Q3 and Q1 and feeding this to clear input line be-
cause binary representation of 10 is 1010
And we see Q3 and Q1 are 1 here, if we give NAND of these two bits to clear input then counter will be clear at
10 and again start from beginning.
Important point: Number of flip flops used in counter are always greater than equal to (log2 n) where n=number
of states in counter.
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CITS : E & H - Electronics Mechanic - Lesson 9 - 29
