Sequential Logic PDF

# REGIMEN ## TEMA 4 ### Introduction The Sequential Logic is the method of ordering actions, reasoning, and expression of the automation of machinery, equipment, and processes. And their interaction with the human being. This gives us consequently the binomials, man-machine, man-process. Each digi...

# REGIMEN ## TEMA 4 ### Introduction The Sequential Logic is the method of ordering actions, reasoning, and expression of the automation of machinery, equipment, and processes. And their interaction with the human being. This gives us consequently the binomials, man-machine, man-process. Each digital system must have combinational circuits, most systems also include memory elements, which require that the system be described in terms of sequential logic. The memory elements are capable of storing binary information within them. The binary information stored in the memory elements at a given time defines the state of the sequential circuit. The sequential circuit receives the binary information from the external inputs. There are two types of sequential circuits. Their classification depends on the timing of their signals. A synchronous sequential circuit is a system whose behavior can be defined based on the knowledge of its signals at discrete points in time. The behavior of an asynchronous circuit depends on the order in which the input signals change and can be affected at a given point in time. In asynchronous systems, the memory elements consist of logic gates whose propagation delays constitute the required memory. Thus, an asynchronous sequential circuit can be considered a combinational circuit with feedback. A synchronous logic sequential system, by definition, can use signals that affect the memory elements only at discrete points in time. One way to achieve this is to use limited duration pulses throughout the system so that the pulse amplitude represents logic 1 and another pulse amplitude (or the absence of a pulse) represents logic 0. Synchronous sequential circuits that use clock pulses at the inputs of the memory elements are called clocked sequential circuits. ### Logic Sequential In sequential logic, unlike combinational logic, a basic element called a flip-flop is used. The flip-flop is a memory element that stores a bit of information. Some texts use this name to refer to latches, but in most publications, a distinction is made between flip-flop and latch. This latter term is the one that is translated as latch. As stated before, sequential logic circuits are basically divided into two groups: asynchronous circuits and synchronous circuits. The former can change the states of their outputs as a result of changes to the states of the inputs, while synchronous circuits can change the state of their outputs at discrete points in time under the control of a clock signal. ### Flip-Flops Unlike latches, flip-flops are synchronous devices and the state of their outputs is controlled at discrete time points by a clock signal (pulses). Like latches, there are several types and their applications are diverse. Flip-flops are devices that respond to a clock signal during the changes from 1 to 0 logic or 0 to 1 logic, depending on the type of flip-flop. To make the flip-flops respond to the change in the clock signal, it is necessary to implement a circuit that detects the rising or falling edge of the clock signal. A master-slave flip-flop contains two latches, one acting as master and the other as slave. During the transition of the clock signal from 1 to 0 logic, the inputs are used to determine the output of the master. When the clock signal goes from 0 to 1 logic, the state of the ==End of OCR for page 9==