3 BIT DOWN COUNTER SUBJECT: DIGITAL ELECTONICS CODE: COLLEGE: BVM ENGINEERING COLLEGE COLLEGE CODE:008 ELECTRONICS & TELECOMMUNICATION DEPT

 Circuits for counting events are frequently used in computers and other digital systems.  Since a counter circuit must remember its past states, it has to possess memory.  The number of flip-flops used and how they are connected determine the number of states and the sequence of the states that the counter goes through in each complete cycle.

3  Asynchronous (ripple) They use the O/P of one FF to generate the clock transition on another FF (s).  Synchronous Clock inputs on each FF are connected together.

Other categories  Asynchronous (ripple) counter  Synchronous counter  Ring counter  Johnson counter  Decade counter  Up–down counter

5 USES OF COUNTER  Counters can act as simple clocks to keep track of “time”  All processors contain a program counter, or PC Programs consist of a list of instructions that are to be executed one after another (for the most part). The PC keeps track of the instruction currently being executed. The PC increments once on each clock cycle, and the next program instruction is then executed.

 Consider JK excitation table.  In order to do that, the characteristics of JK flip-flop must be required.  The following diagram shows the JK flip- flop characteristics.

 Given below is the table of 3 bit down counter’s counting sequence.

 Hence, now we can represent the value of J ₀, J ₁, J₂, K₀, K₁ and K₂ by K-Map.