LATCHES & FLIPFLOPS UNIT-2 Mohammad Asif Iqbal Assistant Professor, Deptt of ECE, JETGI, Barabanki
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LATCHES & FLIPFLOPS
UNIT-2
Mohammad Asif IqbalAssistant Professor, Deptt of ECE,JETGI, Barabanki
STORAGE ELEMENTS
BEFORE STARTING LET’S RECALL NAND GATE
A B Y
0 0 1
0 1 1
1 0 1
1 1 0
BASIC STORAGE ELEMENT
0
1
1
0
1
LATCH
FLIP-FLOP
CLOCK
S
R
Q
Q’
=1
=0
0
1
=1
=0
0
0
1
0
0 0 1 0
FLIP-FLOP
CLOCK
S
R
Q
Q’
=0
=1
1
0
=0
=1
0
0
0
1
0 0 1 0
0 1 0 1
0 0 0 1
FLIP-FLOPINPUT OUTPUT
S R Q Q’
0 0 NO CHANGE
0 1 0 1
1 0 1 0
1 1 ? ?
S
R
CLOCK
Q’
Q SET
RSET
=1
=1
0
0=1
=1INDETERMINANT
CHARACTERISTIC TABLE
BLOCK DIAGRAM REPRESENTATION
S
R
Q’
Q
CLOCK
DD Q Q’
0 0 1
1 1 0
Q Q(n+1) D
0 0 1
1 1 0
Q(n) D Q(n+!)
0 0 1
1 1 0
D FLIP-FLOPD Q Q’
0 0 1
1 1 0
Q Q(n+1) D
0 0 1
1 1 0
Q(n) D Q(n+!)
0 0 1
1 1 0
CHARACTERISTIC TABLE
TRUTH TABLE
EXCITATION TABLE
J K FLIP-FLOP
J
K
CLOCK
Q
Q’
=1
=0
1
0
=1
=1
=1
=0=0
=1 =0
=1
WAVE FORM REPRESENTATION
(t)T 2T
CLOCK
Q
0
1
NOW, changes at I/P will affect O/PAny change at I/P
will not effect O/P
0
1
RACE AROUND CONDITION
SOLUTION OF RACE AROUND CONDITION
(t)T 2T
CLOCK
Q
0
1
0
1
T F
PROPAGATION DELAY
FINAL SOLUTION……
(t)T 2T
CLOCK
Q
0
1
0
1
PROBLEMS
Q:- Determine the output of PGTclocked SR flip flop which Qinitially 0 for the given inputwaveforms
QQ’
Q:- Determine the output of PGTclocked SR flip flop which Qinitially 1 for the given inputwaveforms.
Master Slave Flip Flop
K
JQ
Q’=0
=10 0 1 1
=1
=1
1
0
=1
=0 =1
=0=0
=1
THANK YOU!
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