Digital Logic · Unit 9
Sequential Circuits and Counters
Exam-focused notes for Sequential Circuits and Counters (Digital Logic, BIT103): what the TU syllabus asks and how it has actually been tested, with 10 solved past questions from this unit.
What this unit covers
- Sequential circuit design methodology
- State diagrams and excitation tables
- Ripple counters and synchronous counters
- Binary counters and modulo counters
- Ring counter and Johnson counter
- Up-down counters
- Counter design using flip-flops
Up-down counters
What is counter?Design a 3-bit synchronous up-down counter along with state diagram and timing sequence.[2+8]
--- A counter is a sequential logic circuit that goes through a prescribed sequence of states upon the application of input pulses (clock pulses). It is used to count the number of occurrences of an event or to generate a specific sequence of states. Key fe...
Full solved answer →Counter design using flip-flops
Define parallel counter. Design MOD-12 synchronous up counter along with state diagram, timing sequence and timing diagram.[10]
--- A parallel counter (also called a synchronous counter) is a sequential digital circuit in which all flip-flops receive the clock pulse simultaneously. Unlike ripple (asynchronous) counters where each flip-flop triggers the next, in a synchronous counter...
Full solved answer →Design Mod-5 synchronous counter using T- flip flop. [5]
A Mod-5 counter counts from 0 to 4 (5 states: 000 → 001 → 010 → 011 → 100 → 000) and then resets. We need 3 T flip-flops (Q2, Q1, Q0) to represent 5 states. --- State Q2 Q1 Q0 Next Q2 Next Q1 Next Q0 ----------------------------------------------- 0 0 0 0 0...
Full solved answer →Design Mod-3 synchronous counter. [5]
A Mod-3 counter counts in the sequence: 0 → 1 → 2 → 0 → 1 → 2 → ... It requires 2 flip-flops (since 2^2 = 4 ≥ 3) and uses JK flip-flops (standard design approach). --- Present State Next State :---::---: Q1 Q0 Q1+ Q0+ 0 0 0 1 0 1 1 0 1 0 0 0 1 1 X X (invali...
Full solved answer →Explain with state diagram and excitation table for 3-bit binary counter. [5]
A 3-bit binary counter counts from 000 to 111 (0 to 7) in sequence and then resets back to 000. It uses 3 flip-flops (Q2, Q1, Q0) where Q2 is the MSB and Q0 is the LSB. --- The counter cycles through 8 states in order: Each arrow represents a clock pulse tr...
Full solved answer →Ring counter and Johnson counter
Differentiate between ring counter and Johnson counter. [5]
--- A ring counter is a shift register with the output of the last flip-flop connected directly (straight connection) back to the input of the first flip-flop. - Only one flip-flop is HIGH (1) at any given time; all others are LOW (0). - For n flip-flops, i...
Full solved answer →What is ring counter? Explain ring counter with diagram, timing sequence and timing diagram.[10]
A ring counter is a type of shift register in which the output of the last flip-flop is connected back (fed back) to the input of the first flip-flop, forming a closed loop or "ring." It is also called a circular shift register. A single logic HIGH (1) bit ...
Full solved answer →Sequential circuit design methodology
Design a sequential circuit using JK flip-flop with the help of given state diagram.[10]
Since no specific state diagram image was provided, I will use the standard 3-bit Up Counter state diagram (a very common 10-mark exam question at TU CSIT), which cycles through states: 000 → 001 → 010 → 011 → 100 → 101 → 110 → 111 → 000 --- We have 3 flip-...
Full solved answer →Ripple counters and synchronous counters
Compare the logic of synchronous counter and ripple counter. [5]
Logic of Operation: - Only the first flip-flop receives the external clock pulse directly. - Each subsequent flip-flop is triggered by the output (Q) of the previous flip-flop. - The clock signal "ripples through" from one flip-flop to the next, hence the n...
Full solved answer →Differentiate between synchronous and asynchronous counter.Explain any one synchronous counter.[3+7]
Feature Synchronous Counter Asynchronous Counter --------- Clock Signal All flip-flops are triggered by the same common clock signal simultaneously Flip-flops are triggered one after another; only the first FF receives the clock directly Speed Faster operat...
Full solved answer →Make Unit 9 stick
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