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Digital Electronics
NUMBER SYSTEM
BINARY CODES
BOOLEAN ALGEBRA
K MAPS
COMBINATIONAL CKT
SEQUENTIAL CIRCUITS
INTRODUCTION
CLOCK
BISTABLE MULTIVIBRATOR
DERIVATION of FLIPFLOP circuit
RS FLIPFLOP
RS FLIPFLOP(NAND IMPLEMENTATION)
R'S' FLIPFLOP
Clocking RS LATCH
Other LATCHes
Timing problem in LATCHES
MORE QUESTIONS
TIMING CIRCUITS

 

DOWN COUNTER: (Reverse counting)

Here we’ll be counting in reverse order i.e. count would start from 15 to 0 and again value goes from 0 to 15. We just make a change in the circuit as we give Q bar to the CLK of next flip-flop or we use positive edged flip-flops and give Q to CLK of next flip-flop.

And the output waveform would be as:

Or

And the output waveform would be as:

In both cases we take (Q4 Q3 Q2 Q1) 2 as value of the count

 

 

 

Or

We can just use the same circuit as the UP counter but

Consider the following circuit

 

And we see that this circuit is a UP counter which count from 0 to 7 and then it is reset but the same circuit can also work as DOWN counter when we take count as combination of inverted outputs for each FF. i.e.. Hence output count of the above circuit would go from 7 to 0 and then again it is set to 7.

 

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