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COUNTERS [Synchronous and Asynchronous]
- 1. COUNTERS SYNCHRONOUS & ASYNCHRONOUS Presentation by: C.MURALIDHARAN V.A.SAIRAM A.SUBHA SHREE
- 2. COUNTER The Counter is an electronic circuit that counts the events. The events can be numbers. It can also count the event related to the clock like rising edge(low to high) and trailing edge(high to low) It is a type of sequential logic circuit i.e. The present output depends on the present input and the combination of previous input) Counter can be designed using t-flipflop(which is a special case of JK flipflop).
- 3. TYPES OF COUNTERS Broadly counters can be classified into two types based on the modes of operation. Synchronous Asynchronous In Synchronous mode, all the flip-flops receive input at the same time and produce output at the same time. Synchronous counters are counters that use the clock signal at the same time. In Asynchronous mode, the clock is given only to the first flip flop and each flipflop produces output one at a time. The input for the successive flip-flops depends on the previous ones. These counters are also called RIPPLE COUNTERS. These counters can again be categorized as UP and DOWN counters.
- 4. WHY SYNCHRONOUS COUNTERS? The major drawback in asynchronous counters is that they are limited to high frequencies due to the propagation delay. Synchronous counters can be operated at higher frequencies. Synchronous counters are faster in operation. Easy to design. No delay in synchronous counters.
- 5. TABLE OF CONTENTS MOD 4 Asynchronous MOD 4 Synchronous MOD 7 Asynchronous Specialized IC for Counters MOD 8 Asynchronous MOD 8 Synchronous MOD 16 Asynchronous MOD 16 Synchronous Applications of Counter
- 6. MOD 4 ASYNCHRONOUS MOD (fully known as modulus) is nothing but the number of output states of the counter. MOD 4 will have 4 output states produced in asynchronous manner. Now, the number of flip flops(i.e. n) is based on the given formula: 2 = MOD Here we already know that the output state is 4. So 2 =4 implies n=2. 2 flip flops are used to produce the 4 counts in MOD 4 asynchronous counter. 4 output states are nothing but
- 7. O/P-1(01) O/P- 2(10) These are some of the outputs of MOD 4 asynchronous counters. Q0 is LSB(Least Significant Bit) and Q1 is MSB (Most Significant Bit). The first figure represents output 1 with Q1=0 & Q0=1 i.e. 01(Binary for 1) The second figure represents output 2 with Q1=1 & Q0=0 i.e. 10(Binary for 2) O/P-output
- 8. MOD 4 SYNCHRONOUS This is MOD 4 synchronous counter where the count happens in two ways as follows: ascending (UP) or in descending manner (DOWN). These counters are easier than asynchronous counters. Like the previous one,2 flip flops are needed to produce the 4 output states. The difference is that in synchronous counters, the output changes simultaneously due to the common clock pulse and the count is done sequentially in synchronous counter. Here the counter counts from 0 to 3 (00
- 9. O/P-2(10) O/P-3(11) Here are some of the outputs of the MOD 4 synchronous counter with the same Q0 as LSB and Q1 as MSB The first figure represents output 2(10 in binary) The second figure represents output 3(11 in binary)
- 10. MOD 7 ASYNCHRONOUS From the title, we came to know that the output state is 7. We know to calculate the number of flip flops from the formula =output state (7) Here 7 is not a multiple of 2, hence we may get confused about how to choose the number of flip flops when the output state is not equal to 2 In that case we choose a number which is a multiple of 2, greater and nearer to 7. the number that satisfies all the above conditions is 8(23 ). Hence, we conclude that we should choose the least possible number of flip-flops. It is not fully sequenced. These types of counters are called truncated counters. All the outputs of the flipflop are 2
- 11. Here we consider MOD 7 as an example. After count 6, it automatically tries to go to count 7 (111 in binary) which is not required here. In that case the value 1 of all the flip-flops moves to the NAND gate. So the output is 0 which is again sent to the clear pins of the respective flip flops that use a NAND gate to reset to the required count between 0 to 5. A Clear pin is a special pin present in T flip-flop (special of JK flip-flop). Once it is activated it resets the flip flop(0) irrespective of a past condition. The clear pin is activated by a logic low (0) signal. In this case, all the flip flop gets reset and the value goes to 0. Hence MOD 7 is achieved. This gave the way for the IC 74293 that is embedded with 4 flip flops and a NAND gate. NAND gate is mainly used to detect the output 1 which is generated by the flip- flops. WORKING OF THE TRUNCATED COUNTERS
- 12. O/P-4 O/P-5 The output 4(100 in binary) and output 5(101 in binary) of MOD 7 asynchronous counter is represented here.
- 13. MOD 8 ASYNCHRONOUS MOD 8 Asynchronous counter can be designed using 3 flip-flops. It is a fully sequenced counter. 2 =8 implies n=3 It counts from 000 to 111 i.e. 0 to 7
- 14. O/P-2 O/P-6 LSB is Q0 and MSB is Q2 The first figure represents output 2(010 in binary) The second figure represents output 6(110 in binary)
- 15. MOD 8 SYNCHRONOUS MOD 8 synchronous counter is designed using 3 flip flops. It is also a fully sequenced counter which counts in a sequential manner from 0 to 7 or 7 to 0. The second flipflop gets its input from the output of first flipflop (Q1), the third flipflop gets its input from the outputs of the first and second flipflop through a AND gate.
- 16. O/P-5 O/P-7 The output 5(101 in binary) and output 7(111 in binary) of MOD 8 synchronous counter is given here.
- 17. MOD 16 ASYNCHRONOUS MOD 16 asynchronous counter is designed using 4 flip-flops as per the formula. It counts from 0000 to 1111 i.e. 0 to F(in hexadecimal) The outputs of all the four flip-flops are connected to a four-pin NAND gate Its output is sent to the clear pins of all the flip-flops. The counter has to reset back to 0(0000) after counting 15(1111). In the case of 15, the NAND gate receives 1 in all inputs, it produces an output of 0. This logic 0 activates the clear pin of all flipflops resetting them to count 0.
- 18. O/P-13 O/P-14 Here Q1 is LSB and Q4 is MSB The first picture represents output 13 (decimal value) i.e.1101 in binary. It is converted into hexadecimal value as d and displayed. Similarly the next output 14 i.e. 1110 in binary is displayed as E (Hexadecimal value).
- 19. MOD 16 SYNCHRONOUS MOD 16 synchronous counter can be constructed using 4 flipflops. It can do either up count operation (0-15) or down count operation (15- 0). The second flipflop gets its input from the output of first flipflop (Q1), the third flipflop gets its input from the outputs of the first and second flipflop through a AND gate. The fourth flipflop receives its input from the output of first, second and third flipflops. A trick is to use the output of the previous flipflop along with the output of the previously connected AND gate.
- 20. O/P 12 O/P 14 Here again, Q0 is LSB and Q3 is MSB The first figure represents output 12 i.e.1100 in binary (C in hexadecimal) The second one represents output 14 i.e.1110 in binary (E in hexadecimal)
- 21. UP-DOWN COUNTERS As the name suggests it counts in both ways i.e. from low to high and also from high to low. So these are also called bidirectional counters. They are built using JK flip-flops. Here it is a 4 bit UP-DOWN counter. It counts from 0 to F on one side and F to 0 on the other side. These are self reversing and used in clock divider circuits.
- 22. COUNTS FOR UP-DOWN COUNTER Some of the output counts of the UP-DOWN counter
- 23. APPLICATIONS OF COUNTERS Frequency counters Digital clocks Analog to digital converter Calculators etc.,
- 24. 1) C.MURALIDHARAN Assistant Professor, Biomedical Engineering, Rajalakshmi Engineering College 2) A.SUBHA SHREE Student, Biomedical Engineering, Rajalakshmi Engineering College 3) V.A.SAIRAM Student, Biomedical Engineering, Rajalakshmi Engineering College
- 25. REFERENCES: https://www.electronics-tutorials.ws/counter/count_3.html https://www.electronicshub.org/synchronous-counter/ https://www.electronicshub.org/asynchronous-counter/
- 26. THANK YOU