Introduction to Sequential Circuit
Tags: #◇Computer Science #◇CSARCH1 #◇Conceptual #◇M5
◇Overview
Sequential circuits act as storage elements and possess memory. The output (or next state) in a sequential circuit is a function of the present state and the input.
- The system must have at least one feedback path from the memory element to the system inputs.
Synchronous vs. Asynchronous Sequential Circuits
- Synchronous sequential circuit: Behavior is defined at discrete instants of time. Synchronization is achieved by a timing device called a clock generator, providing a periodic train of clock pulses (clock or clk).
- Clock pulses can be level triggered (positive or negative) or edge triggered (positive or negative).
- Asynchronous sequential circuit: Behavior depends on the order in which input signals change. It can be affected at any instant of time. There is no single system clock, and transitions are defined in units of gate delay.
◇Key Definitions
Memory Elements: Latch vs. Flip-Flop
- Basic memory elements are capable of storing one bit of information (0 or 1).
- Latch: Based on level signal, primarily used in asynchronous sequential circuits.
- Flip-Flop: Based on edge trigger, primarily used in synchronous sequential circuits.
Types of Flip-Flops
There are 4 major types of Flip-Flops, differing in the number of inputs and how inputs affect the binary state:
-
SR Flip-Flop (Set-Reset):
- S=0, R=0: No change
- S=0, R=1: Reset (Q=0)
- S=1, R=0: Set (Q=1)
- S=1, R=1: Indeterminate
- Characteristic Equation:
Q(t+1) = S + R'Q(where S and R cannot both be 1)
-
JK Flip-Flop:
- J=0, K=0: No change
- J=0, K=1: Reset (Q=0)
- J=1, K=0: Set (Q=1)
- J=1, K=1: Toggle
- Characteristic Equation:
Q(t+1) = JQ' + K'Q
-
D Flip-Flop (Data):
- D=0: Follows input (Q=0)
- D=1: Follows input (Q=1)
- Characteristic Equation:
Q(t+1) = D
-
T Flip-Flop (Toggle):
- T=0: No change
- T=1: Toggle
- Characteristic Equation:
Q(t+1) = T'Q + TQ' = T ⊕ Q
◇References & Navigation
- Previous Topic: ◇Hardware Description Language Structural Modelling
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- Related Notes: ◇Combinational Circuit - Design, ◇Sequential Circuit - Analysis
ACTIVE RECALL VERIFICATION
Select an answer to verify conceptual comprehension and reveal the technical rationale.
What defines a sequential circuit's output?
What is required in a sequential system that differentiates it from a combinational system?
What achieves synchronization in a synchronous sequential circuit?
What is the primary difference between a latch and a flip-flop?
In an SR Flip-Flop, what happens when both S and R inputs are 1?
What is the defining characteristic of a JK Flip-Flop when both J and K are 1?
Which flip-flop simply follows its input at the next clock edge?
What is the state equation for a D Flip-Flop?
What does an asynchronous sequential circuit's behavior depend upon?
In a T (Toggle) Flip-Flop, what is the next state when T=0?