Page 52 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Counter Classification
Counters are broadly divided into two categories

1 Asynchronous counter
2 Synchronous counter
Asynchronous Counter
In asynchronous counter we don’t use universal clock, only first flip flop is driven by main clock and the clock input
of rest of the following flip flop is driven by output of previous flip flops. We can understand it by following diagram

It is evident from timing diagram that Q0 is changing as soon as the rising edge of clock pulse is encountered,
Q1 is changing when rising edge of Q0 is encountered(because Q0 is like clock pulse for second flip flop) and
so on. In this way ripples are generated through Q0,Q1,Q2,Q3 hence it is also called RIPPLE counter and serial
counter. A ripple counter is a cascaded arrangement of flip flops where the output of one flip flop drives the clock
input of the following flip flop.
Synchronous Counter

Unlike the asynchronous counter, synchronous counter has one global clock which drives each flip flop so output
changes in parallel. The one advantage of synchronous counter over asynchronous counter is, it can operate on
higher frequency than asynchronous counter as it does not have cumulative delay because of same clock is given
to each flip flop. It is also called as parallel counter.

From circuit diagram we see that Q0 bit gives response to each falling edge of clock while Q1 is dependent on
Q0, Q2 is dependent on Q1 and Q0 , Q3 is dependent on Q2,Q1 and Q0.
Decade Counter
A decade counter counts ten different states and then reset to its initial states. A simple decade counter will count
from 0 to 9 but we can also make the decade counters which can go through any ten states between 0 to 15(for
4 bit counter).

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CITS : E & H - Electronics Mechanic - Lesson 9 - 29