Analysis and Synthesis of Synchronous Sequential Circuit
The analysis of a synchronous sequential circuit
is the process of determining the functional relation that exists between its
outputs, and its internal states. The contents of all the flip flops in the
circuit combined determine the internal state of the circuit. Thus, if the
circuit contains n flip flops. It can be in one of the 2n states.
Knowing the present state of the circuit and the input values at any time t, We
should be able to derive its next state (i.e.. the state at time t+1) and the
output produced by the circuit at t.
A sequential circuit can be described completely
by a state table that is very similar to the ones shown for flip flops
For a circuit can be 2n rows in the
state table. If there are m inputs to the circuit, there will be 2n
column in the state table. At the intersection of each row and column, the next
stable and the output information are recorded. A state diagram is a graphical
representation of the state table in which each state is represented by a
circle and the state transitions are represented by arrows between the circles.
The input combination that brings about the transition and the corresponding
output information are shown on the arrow. Analysing a sequential circuit thus
corresponds to generating the state table and the state diagram for the
circuit. The state table or state diagram can be used to determine to output
sequence generated by the circuit for a given input sequence if the initial
state it known. It is important to note that for proper operation, a sequential
circuit must be in its initial state before the inputs to it can be applied.
Usually the power up circuits are used to initialize the circuit to the
appropriate state when the never is turned on.
circuit analysis (a) circuit (b) next state and output tables (c) transition
table (d) state diagram (e) timing diagram for level input (f) timing diagram
for synchronous pulse input.