Counters

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 Counters

 a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock. The most common type is a sequential digital logic circuit with an input line called the clock and multiple output lines. The values on the output lines represent a number in the binary or BCD number system. Each pulse applied to the clock input increments or decrements the number in the counter.


A counter circuit is usually constructed of a number of flip-flops connected in cascade. Counters are a very widely used component in digital circuits, and are manufactured as separate integrated circuits and also incorporated as parts of larger integrated circuits.


There are 2 types

1)       Synchronous

 

2)      Asynchronous

                      


How to create   Asynchronous  4 bit Up Counter &  Asynchronous  4 bit down Counter



                                 UP COUNTER            DOWN COUNTER




 

BCD or Decade Counter

 A BCD counter or decade counter can be constructed from a straight binary counter by terminating the "ripple-through" count when the count reaches decimal 9 (binary 1001). Since the next toggle would produce 1010, that drives both X1 and X3 high, and since they are the inputs to the NAND gate, the output of the NAND goes low. This zero output to the asynchronous clear line will clear the registers and start the count after 9




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