Asynchronous and Synchronous Counters

What is an asynchronous counter?​

• Output is free from the clock signal

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• ​Supplied with different clock signals, there may be delay in producing output.

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• ​The clock inputs of all flip flops are cascaded and the D input of each flip flop is connected to a state output of the flip flop.

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• ​The flip flop will toggle at each active edge or positive edge of the clock signal.

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• ​The clock input from Q' output of the previous flip flop.

What is a synchronous counter?​

• All flip -flops are simultaneously clocked by and external clock.

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• Synchronous counters are faster than asynchronous counters.

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• ​Synchronous counters do not suffer from the ripple effect that asynchronous counters do.

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• ​​They require more logic.

​1.) Label the counters in green.

​2.) Notice the difference between these two.

​3.)

​1.) Label the clock pulses.

​2.) Label the count (at the bottom

3.) Add dotted lines between pulses starting from pulses down to align with the count at the bottom.

Multiple Choice

What is happening with Q0? (red arrows)

• Toggles on Falling Edge of CLOCK & Q0 = 1

• Toggles on Falling Edge  of CLOCK

• Toggles on Falling Edge of CLOCK & Q0 = 1 & Q1 = 1

• Nothing, it remains low all the time.

Multiple Choice

What is happening with Q1? (purple arrows)

• Toggles on Falling Edge of CLOCK & Q0 = 1

• Toggles on Falling Edge  of CLOCK

• Toggles on Falling Edge of CLOCK & Q0 = 1 & Q1 = 1

• Nothing, it remains low all the time.

Multiple Choice

What is happening with Q2? (green arrows)

• Toggles on Falling Edge of CLOCK & Q0 = 1

• Toggles on Falling Edge  of CLOCK

• Toggles on Falling Edge of CLOCK & Q0 = 1 & Q1 = 1

​1.) Add the label for the function of each flip flop.

​2.) Circle the external clock. 

Multiple Choice

Ripple counters are also called ______?

• SSI Counter

• Asynchronous counters

• Synchronous counters

• mode counter

Multiple Choice

A ring counter with 5 flip flops will have ____ states,

• 5

• 10

• 32

• 12