Skip to Content
Introduction to Digital Systems: Modeling, Synthesis, and Simulation Using VHDL
book

Introduction to Digital Systems: Modeling, Synthesis, and Simulation Using VHDL

by Mohammed Ferdjallah
July 2011
Intermediate to advanced content levelIntermediate to advanced
225 pages
6h 22m
English
Wiley
Content preview from Introduction to Digital Systems: Modeling, Synthesis, and Simulation Using VHDL

9.2 SYNCHRONOUS SEQUENTIAL CIRCUITS

In a combinational circuit, the outputs at any point in time are fully determined by the inputs present at that point in time. In a sequential logic circuit, the outputs depend not only on the present inputs but also on the past behavior of the circuit. Thus, a sequential logic circuit consists of a combinational circuit and memory elements that form a feedback system, as illustrated in Figure 9.1.

The sequential circuits described in Chapter 8 perform simple functions such as shifting and counting. Registers shift data inputs in response to a clock signal. Similarly, counters generate a predetermined sequence of states and have no inputs other than the initial conditions and the clock signal. The counters designed in Chapter 8 were constructed by cascading flip-flops to count in an orderly fashion. Changing the count order requires a sequence of data input. The design methods designed so far are not adequate to design a complex sequential circuit.

A sequential circuit which has additional inputs that may change its present state is also referred to as afinite-state machine (FSM). In general, the output sequence of an FSM depends on the input sequence and the present state of flip-flops of the FSM. There are two classes of sequential circuits, synchronous and asynchronous. If a clock signal is used to control the operation of a sequential circuit, the circuit is known as a synchronous sequential circuit. Asynchronous sequential circuits do not ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Digital Systems Design with FPGAs and CPLDs

Digital Systems Design with FPGAs and CPLDs

Ian Grout
Synthesis of Arithmetic Circuits: FPGA, ASIC and Embedded Systems

Synthesis of Arithmetic Circuits: FPGA, ASIC and Embedded Systems

Jean-Pierre Deschamps, Gery J.A. Bioul, Gustavo D. Sutter

Publisher Resources

ISBN: 9780470900550Purchase book