TOPIC : Introduction to Sequential Circuits UNIT 1: Modeling and Simulation Module 4 : Modeling Sequential Circuits

Sequential Circuits Digital electronics ◦ Combinational logic circuits ◦ Sequential logic circuits Combinational Logic circuits - output depends on the inputs Sequential logic - output depends on previous outputs and also the applied inputs

General Sequential Circuit It can be represented as a combination of combinational circuit and memory element With Some feedback.

Sequential Circuits contd … The memory elements are devices capable of storing binary information. The binary information stored in the memory elements at any given time defines the state of the sequential circuit. The input and the present state of the memory element determines the output. A sequential circuit is specified by a time sequence of inputs, outputs, and internal states.

Types of Sequential Circuits Two types of sequential circuits ◦ Synchronous sequential circuits ◦ Asynchronous sequential circuits Their classification depends on the timing of their signals

Asynchronous Sequential Circuits It is a sequential circuit whose behavior depends only on the order in which its input signals change and can be affected at any instant of time.

Contd … State transition occurs when there is an input change (no clock pulses). Delay elements are either latches ( unclocked ) or time- delay elements. Quite often it resembles a combinational circuit with feedback. More difficult to design, verify, or test.

Synchronous Sequential Circuits It is a sequential circuit in which the output depends on present state and present inputs at the clocked instances only.

Contd … Have a clock signal as one of their inputs. Uses logic gates and flip-flop storage devices. Flip-flops are storage elements that are employed to change their binary value only at specific instants of time. They are stable and their timing of events can be easily broken down into independent discrete events.