The basic building block of sequential logic circuit is-
Flip flop
Understanding Sequential Logic Circuits
Digital logic circuits can be broadly classified into two main types: combinational and sequential circuits. Combinational circuits produce an output based solely on the current input values. Sequential circuits, on the other hand, produce an output that depends not only on the current inputs but also on the history of past inputs. This ability to remember past inputs is achieved by incorporating memory elements.
Basic Building Block of Sequential Logic
The fundamental difference between combinational and sequential circuits lies in the presence of memory. Sequential circuits require components that can store information over time. Let's look at the provided options:
- OR gate: This is a basic combinational logic gate. Its output depends only on its current inputs. It has no memory function.
- NAND gate: This is also a basic combinational logic gate. Like other gates, its output is determined solely by its current inputs and it cannot store information.
- AND gate: Another basic combinational logic gate. It provides an output based only on the current inputs and lacks memory.
- Flip flop: A flip-flop is a bistable multivibrator, meaning it has two stable states (typically representing 0 and 1). It is a fundamental memory element. A flip-flop can store one bit of binary information and retain that state until a trigger signal causes it to change.
Because sequential logic circuits must have memory to store past information, the basic building blocks must be elements capable of storing a state. Flip-flops are the most fundamental elements that provide this memory function in digital circuits. Complex sequential circuits, such as counters, registers, and state machines, are constructed using flip-flops along with combinational logic gates.
Therefore, the basic building block that gives sequential logic circuits their characteristic memory property is the flip-flop.
Revision Table: Combinational vs. Sequential Logic
| Feature | Combinational Logic | Sequential Logic |
|---|---|---|
| Output depends on | Current inputs only | Current inputs AND past inputs (state) |
| Contains memory elements | No | Yes |
| Basic Building Blocks | Logic gates (AND, OR, NOT, NAND, NOR, XOR, XNOR) | Flip-flops, Latches (memory elements) + Logic gates |
| Example Circuits | Adders, Subtractors, Multiplexers, Decoders | Counters, Registers, State Machines |
Additional Information on Flip-flops
Flip-flops are synchronous memory elements, meaning their state changes only at specific times determined by a clock signal. There are different types of flip-flops, including:
- SR (Set-Reset) Flip-flop
- JK Flip-flop
- D (Data) Flip-flop
- T (Toggle) Flip-flop
Each type has different input configurations and behavior, but their core function is to store one bit of data and provide the necessary memory for sequential operations.
Important Questions from Flip-Flop
What type of Flip Flop is used in Counters?
What is the characteristic of a master-slave flip-flop?
A single flip-flop is a modulo __________ counter.
For a JK Flip‐flop
A. When J = 0, K = 1, Q n+1 = 0
B. When J = 1, K = 1, Q n+1 = 1
C. When J = 1, K = 1, Q n+1 =\(\rm \overline{Q_n}\)
D. When J = 1, K = 0, Q n+1 = 1
E. When J = 1, K = 0, Q n+1 = 0
Choose the correct answer from the options given below:
In a JK flip flop, if J = K, then resulting flip flop is ______.
