The storage elements (memory) used in clocked sequential circuits are called flip-flops. Their timing is easily broken down into independent discrete steps,Įach of which can be considered separately.īlock diagram - Synchronous clocked sequential circuit The design of synchronous circuits is feasible because they seldom manifest instability problems Within the circuit and the resulting updating of stored values is synchronized to the occurrence of clock pulses. They are called synchronous circuits because the activity Synchronous sequential circuits that use clock pulses to control storage elements are called clocked sequential circuits and are the type most Within the circuit, and other signals (external inputs and otherwise) determine what changes will take place affecting the storage elements and the outputs.Įxample, a circuit that is to add and store two binary numbers would compute their sum from the values of the numbers and store the sum at the occurrence of a clock pulse. The clock pulses determine when computational activity will occur The clock pulses are distributed throughout the system in such a way that storage elements are affected only with the arrival of each pulse. Synchronization is achieved by a timing device called a 'a clock generator', which provides a clock signal having the form of a periodic train of 'clock pulses'. Synchronous sequential circuit employs signals that affect the storage elements at only discrete instants of time. They use a clock pulse for controlling the output. Synchronous sequential circuit: A system whose behavior can beĭefined from the knowledge of its signals at discrete instants of time. In which the inputs change, The storage elements commonly used in asynchronous sequential circuits are time-delay devices. There are two main types of sequential circuits, and their classification is a function of the timing of their signals.Īsynchronous sequential circuit: A system whose behavior depends upon the input signals at any instant of time and the order Thus, a sequential circuit is specified by a time sequence of inputs, outputs, and internal states. The next state of the storage elements is also a function of external inputs and the present state. The block diagram demonstrates that the outputs in a sequential circuit are a function not only of the inputs, but also of the present state of the storage elements. These external inputs also determine the condition for changing the state in the storage elements. The sequential circuit receives binary valued inputs from external sources, this together with the present state of the storage elements determines the binary value of the outputs. This information that is stored at any time defines the state of the sequential circuit at that time. Storage elements are devices capable of storing binary information. Sequential Logic consists of combinational circuit to which storage elements are connected to form a feedback path. The actions of these circuits depend on a range of basic sub-circuits.Although every digital system is likely to have some combinationalĬircuits, most systems encountered in practice also include storage elements which require that the system can be described in terms of sequential logic. Examples of such circuits include clocks, flip-flops, bi-stables, counters, memories, and registers. In other words the output depends on a SEQUENCE of events occurring at the circuit inputs. In these circuits the output depends, not only on the combination of logic states at its inputs, but also on the logic states that existed previously. Use Module 5 to learn about digital circuits that use SEQUENTIAL LOGIC.

For this reason these circuits are called combinational logic circuits. The logic circuits discussed in Digital Electronics Module 4 had output states that depended on the particular combination of logic states at the input connections to the circuit.

Test your knowledge of Sequential Logic.Connecting digital components together.

D Type & JK flip-flops using CMOS technology.

Sequential logic circuit