2.1 Seven Segment Display                     Seven segment display also known as seven segment indicator ,isan electronic device  that displaydecimal numbers. It is used in many things; for example digital watches  , electronic meters ,and basic calculators.The seven segment consists of seven LEDs( light emitting diode) arrangedin rectangular fashion. Each of the seven LEDs is called segment because when illuminatedthe segment forms parts of numerical digit to be displayed.

An additional 8thLED is sometimes used within the same package thus allowing the indication of adecimal point ,when two or more seven segment display are connected together todisplay numbers greater than ten.The display common pin isgenerally used to identify which type of seven segment display it is .As each LEDhas two connecting pins, one called the Anode and the other called Cathode .thedifference between the Common Anode and the Common Cathode is the way ofconnecting of the seven segments .

                                      2.2 Counters          Counters arespecially designed synchronous sequential circuits. They are usuallyconstructed of a number of flip flops connected in cascade, and they are very widelyused for measuring frequency and time. Counters are also similar to shift registers and other combinational circuits.

Counters are also known as digital circuit or timers. They are examplesfor flip flop applications ;and here is an  example of how counter works ;4-bit counter is consists of 4 stages of cascaded J-K flip-flops. Thisis a binary counter, since the output is in binary system format, i.e., onlytwo digits are used to represent the count, i.

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e., ‘1’ and ‘0’.  With only4 bits, it can only count up to ‘1111’, or decimal number 15.The output of counters is based on the clockpulse application it can be used to count the number of pulses.

We have two types of counters; the first one is when the counter hasonly one clock ip  given to all flip flopsit is a synchronous counter, otherwise if the counter op the flip flops is theclock signal nearby one it is asynchronous counter.  (You should write few (two to three)paragraphs about the counters).   2.3 Types of Counters  2.

3.1 Asynchronous counter In a 2 bit asynchronous counter, the exterior clock is connectedto the clock of the first flip flop and it changes the state at a decreasingedge of every clock pulse, however in the second flip flop it changes only whenit is activated by the decreasing edge of Q of the first flip flop. The circuitdiagram of the two-bit ripple counter includes four different states each oneis consisting with a count value. Likewise, a counter with n flip flops can have2n states. The number of state in a counter is called as its mod number. Therefore,a two-bit counter is a mod-4 counter.2.3.

2 synchronous counterIn the synchronous counter , the CLK i/ps of all the FFs are connectedtogether and are activated by the i/p pulses. So, all the FFs change statesinstantaneously. The circuit diagram below is a three bit synchronous counter.The inputs J and K of flip-flop0 are connected to HIGH.

Flip-flop 1 has its J&K i/ps connected to the o/p of flip-flop0 (FF0), and the inputs J & Kof flip-flop2 (FF2) are connected to the o/p of an AND gate that is fed by theo/ps of flip-flop0 and flip-flop1. When the both the outputs of FF0 & FF1are HIGH. The positive edge of the fourth CLK pulse will cause FF2 to alter itsstate because of the AND gate.

In the end this issome proptes for each one Asynchronouscounters:a. Are also known as ripple counters;b. are very simple;c. use the minimum possible hardware (logic gates); employ flip-flops connectedserially, with each one triggering (clocking) the next;d. have an overallcount which ‘ripples’ through, meaning the overall operationis relatively slow;e. require virtually no design.Synchronous counters:a. use interconnected flip-flops, but all are clocked together by the systemclock;b.

use the outputs from the flip-flops, to determine the next states of thefollowing flip-flops (rather than simply clocking them);c. require no settling time due to rippling (as all flip-flops are clockedsynchronously);d. need designing, to determine how the present state of the circuit must beused to determine the next state (i.

e. count);  1.4  Application of Counters Adigital counter is a device that generates binary numbers in a specified countsequence. The counter progresses through the specified sequence of numbers whentriggered by an incoming clock waveform, and it advances from one number to thenext only on a clock pulse. The counter cycles through the same sequence ofnumbers continuously so long as there is an incoming clock pulse. The binarynumber sequence generated by the digital counter can be used in logic systemsto count up or down, to generate truth table input variable sequences for logiccircuits, to cycle through addresses of memories in microprocessor applications,to generate waveforms of specific patterns and frequencies, and to activateother logic circuits in a complex process