5 Synchronous Sequential Logic

Question 1

sequential circuit is specified by:

Answer 1

Thus, a sequential circuit is specified by a time sequence of inputs,
outputs, and internal states

Question 2

State of the sequential circuit:

Answer 2

is defined by the binary elements stored in the memory elements at any given time.

Question 3

Ouput of Sequrntial Circuits is determined how:

and state of memory elements:

Answer 3

The sequential circuit receives binary information from external inputs that,
together with the present state of the storage elements, determine the binary value of
the outputs.

THese external ips also determine the condition for changing the state in the storage elements.

Check block diag.

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.

The next state of the storage elements is also a function of external inputs
and the present state

Question 4

Classification of Sequential Circuits :

Answer 4

There are two main types of sequential circuits, and their classification is a function of
the timing of their signals.

A synchronous sequential circuit is a system whose behavior
can be defined from the knowledge of its signals at discrete instants of time.

The behavior
of an asynchronous sequential circuit depends upon the input signals at any instant of time
and the order in which the inputs change.

Question 5

Storage elements commonly used in Asynchronous Sequential circuits are?
About their capacity:

gate-type asynchronous
systems

Answer 5

are time delay devices.
The storage capability of a time-delay
device varies with the time it takes for the signal to propagate through the device. The internal propagation delay of logic gates is of sufficient duration to produce the
needed delay, these are gate-type asynchronous
systems, logic gates propagation delay provides required delay.

So u can say asynchronous sequential circuit is combinational circuit with feedback. (these feedback can give rise to instability)

Question 6

Synchronous Sequential Circuit storage elements :

Answer 6

The storage elements (memory) used in clocked sequential circuits are called flipflops. A flip-flop is a binary storage device capable of storing one bit of information. In
a stable state, the output of a flip-flop is either 0 or 1. A sequential circuit may use many
flip-flops to store as many bits as necessary

Question 7

Synchronous Sequential Circuit :

Structure:

Answer 7

A synchronous sequential circuit employs signals that affect the storage elements at
only discrete instants of time.
- Synchronization is achieved by a timing device called a clock generator, which provides a clock signal [clock / clk] having the form of a periodic train of clock
pulses .
- These pulses distributed throughout the sys so that the storage elements are affected only at the arrival of each pulse.
- clock pulses determine when
computational activity will occur within the circuit, and other signals determine what changes will take place affecting the storage elements
and the outputs.

Question 8

Clocked Sequential circuits:

Why are they called synchronous circuits?

Answer 8

Synchronous sequential circuits that use clock pulses to control storage
elements are called clocked sequential circuits.
- cuz the activity within the
circuit and the resulting updating of stored values is synchronized to the occurrence of clock pulses.
- feasible design, seldom manifests instability and timing easily broken down into independent discrete steps, each can be considered separately.
- Prior to the occurrence of the clock pulse, the combinational logic forming the next
value of the flip-flop must have reached a stable value

Question 9

Clock interval :

Answer 9

Propagation delays play an important role in
determining the minimum interval between clock pulses that will allow the circuit to
operate correctly

Question 10

Change in flip flop state :

Answer 10

A change in state of the flip-flops is initiated only by a clock pulse transition.
for example, when the value of the clock signals changes from 0 to 1. When
a clock pulse is not active, the feedback loop between the value stored in the flip-flop
and the value formed at the input to the flip-flop is effectively broken because the flipflop outputs cannot change even if the outputs of the combinational circuit driving their
inputs change in value. Thus, the transition from one state to the next occurs only at
predetermined intervals dictated by the clock pulses.