Timing Diagram for Positive Edge-Triggered Flip-Flops

Study Notes

Decade Counters

A decade counter has a modulus of 10 and is used in display applications where BCD is required for conversion to a decimal readout.
A 4-bit counter is required to implement a decade counter, as 2^3 (or 3 flip-flops) is insufficient.

Asynchronous Counters

Asynchronous counters are also known as ripple counters.
The events in an asynchronous counter do not have a fixed time relationship with each other and do not occur at the same time.
In an asynchronous counter, the flip-flops do not change states at exactly the same time because they do not have a common clock pulse.

Synchronous Counters

Synchronous counters have a fixed time relationship with each other and do occur at the same time.
In a synchronous counter, all the bits in the count change synchronously with the assertion of the clock.

Counters

A counter can be constructed by a synchronous circuit or by an asynchronous circuit.
Counters can count up or count down or count up and down depending on the input control.
A counter may have a limited range due to its limited word length.
The count sequence usually repeats itself.
External logic can be used to cause the counter to start at any count and terminate at any count.

Uses of Counters

Counters are typically used to count the number of times that a certain event takes place.
Counters are used to control a fixed sequence of actions in a digital system.
Counters are used to generate timing signals.
Counters are used to generate clocks of different frequencies.

Flip-Flops

Flip-flops can be connected together to perform counting operations.
The number of flip-flops used and the way they are connected determine the number of states (modulus) and the specific sequence of states that the counter goes through during each complete cycle.

Description

Explore the timing diagram for a circuit where the effect of CLK8 or CLK 16 must propagate through four flip-flops before Q3 changes. This quiz focuses on asynchronous decade counters and understanding the modulation of a counter based on the number of flip-flops used.