Synchronous
Sequential Circuit
Chapter 5
Overview
Universal model
System
output
Variables
O0
Om
Er
Excitation
Variables
E0
Combinational
logic
System
Input
Variables
I0
In
S0
Sx
State
Variables
Memory
Flip-
flops
CLOCK
Basic concept
Synchronous sequential circuit memory,usually
consisting of flip-flops,update circuit states
information,
All flip-flops share a common clock pulse input.
The clock input is not a binary value representing
the time of day,but rather a,synchronous” train of
pulses,Synchronous memory changes its data only
at certain time intervals,
The flip-flops can change state only on a clock pulse
edge.
The output of memory (flip-flops) defines the state
of a sequential machine,It implies that the state
variables are the flip-flop outputs,The next-state
equation is the characteristics equation of the flip-
flops used in circuit.
Excitation variables are input to memory (flip-flops),
When flip-flops are used for the system memory,the
excitation variables are the inputs (J-K,R-S,D,T) to
the flip-flops,Excitation variables are generated by
the input combinational logic operating on the state
variables and input variables.
Basic concept
Mealy model machine
E = f( I,St )
St+1 = f( St,E ) flip-flop characteristics equation
O = g( I,St )
Describe a SSC
Combinational
transform
(f)
Memory
M
Combination
al logic
(g)
Input
(I) (E)
CLK
State variables
(S)
Excitation variables Output
(O)
Moore model machine
E = f( I,St )
St+1 = f( St,E ) flip-flop characteristics equation
O = g( St )
Describe a SSC
Combinational
transform
(f)
Memory
M
Combinational
logic
(g)
Input
(I) (E)
CLK
State variables
(S)
Excitation variables Output
(O)