- Sequential circuits use a periodic clock signal to determine when to store values from combinational logic circuits. - The basic storage element is a flip flop, which can be constructed from latches. Common types include D, JK, and T flip flops. - Flip flops store their output on either the rising or falling edge of the clock signal. They allow data to be stored indefinitely until the next clock edge. - Multiple flip flops can be combined to store multiple bits of data, forming the basis of computer memory systems. Sequential circuits combine storage from flip flops with additional combinational logic.

1. °2/17/2020

2. Mahasiswa dapat menjelaskan cara
kerja komponen dasar rangkaian
Sequential, yaitu Latch dan Flip-flop.
°2/17/2020

3. Overview
°2/17/2020

4.  Circuits require memory to store intermediate
data
 Sequential circuits use a periodic signal to
determine when to store values.
◦ A clock signal can determine storage times
◦ Clock signals are periodic
 Single bit storage element is a flip flop
 A basic type of flip flop is a latch
 Latches are made from logic gates
◦ NAND, NOR, AND, OR, Inverter
°2/17/2020

5.  Hasil operasi Rangkaian Logika Kombinasional adalah
respon terhadap kombinasi input yang diberikan.
 Hanya bisa menjumlahkan dua bilangan.
 Untuk menjumlahkan bilangan ketiga, diperlukan
penyimpanan informasi hasil penjumlahan
sebelumnya.
▪ Contoh : 2+1 +5
▪ 2 + 1 = 3 maka 3 disimpan di dalam memory, kemudian :
▪ 3 + 5 = 8 (a sequential operation);
 To handle this, we need sequential logic capable of storing
intermediate (and final) results.
°2/17/2020

6. °2/17/2020
Combinational
circuit Flip
Flops
OutputsInputs
Next
state
Present
state
Timing signal
(clock)
Clock
Clock
a periodic external event (input)
synchronizes when current state changes happen
keeps system well-behaved
makes it easier to design and build large systems

7. °2/17/2020
1 1
1 0
0 1
0 0
S R Q Q’
0 1
1 0 Set
1 0 Stable
0 1 Reset
0 0 Undefined
R (reset)
Q
Q
S (set)
° S-R latch made from cross-coupled NORs
° If Q = 1, set state
° If Q = 0, reset state
° Usually S=0 and R=0
° S=1 and R=1 generates unpredictable results

8. °2/17/2020
S
R
Q
Q’
0 0
0 1
1 0
1 1
S R Q Q’
0 1
1 0 Set
1 0 Store
0 1 Reset
1 1 Disallowed
° Latch made from cross-coupled NANDs
° Sometimes called S’-R’ latch
° Usually S=1 and R=1
° S=0 and R=0 generates unpredictable results

9. °2/17/2020
° Occasionally, desirable to avoid latch changes
° C = 0 disables all latch state changes
° Control signal enables data change when C = 1
° Right side of circuit same as ordinary S-R latch.

10. Latch operation
enabled by
C
Input sampling
enabled by gates
°2/17/2020
R’
S’
Q’
Q
C’
Outputs change
when C is low:
RESET and SET
Otherwise: HOLD
Latch is level-sensitive, in regards to C
Only stores data if C’ = 0

11. °2/17/2020
Q
Q’
C
D S
R
X
Y
X Y C Q Q’
0 0 1 Q0 Q0’ Store
0 1 1 0 1 Reset
1 0 1 1 0 Set
1 1 1 1 1 Disallowed
X X 0 Q0 Q0’ Store
0 1 0 1
1 1 1 0
X 0 Q0 Q0’
D C Q Q’
° Q0 indicates the previous state (the previously stored value)

12. °2/17/2020
Q
Q’
C
D S
R
X
Y
0 1 0 1
1 1 1 0
X 0 Q0 Q0’
D C Q Q’
° Input value D is passed to output Q when C is high
° Input value D is ignored when C is low

13. °2/17/2020
E
x
Latches on following
edge of clock
E
D
Q
C
x
z
z
° Z only changes when E is high
° If E is high, Z will follow X

14. °2/17/2020
E
x
Latches on following
edge of clock
E
D
Q
C
x
z
z
° The D latch stores data indefinitely, regardless of
input D values, if C = 0
° Forms basic storage element in computers

15. °2/17/2020
° SR latch is based on NOR gates
° S’R’ latch based on NAND gates
° D latch can be based on either.
° D latch sometimes called transparent latch

16.  Latches are based on combinational gates (e.g.
NAND, NOR)
 Latches store data even after data input has
been removed
 S-R latches operate like cross-coupled inverters
with control inputs (S = set, R = reset)
 With additional gates, an S-R latch can be
converted to a D latch (D stands for data)
 D latch is simple to understand conceptually
◦ When C = 1, data input D stored in latch and output as Q
◦ When C = 0, data input D ignored and previous latch value output at Q
°2/17/2020

17.  Latches respond to trigger levels on control inputs
◦ Example: If G = 1, input reflected at output
 Difficult to precisely time when to store data with
latches
 Flip flops store data on a rising or falling trigger
edge.
◦ Example: control input transitions from 0 -> 1, data input appears at output
◦ Data remains stable in the flip flop until until next rising edge.
 Different types of flip flops serve different functions
 Flip flops can be defined with characteristic
functions.
°2/17/2020

18. °2/17/2020
Lo-Hi edgeHi-Lo edge
° What if the output only changed on a C transition?
C
D Q
Q’
0 0 1
1 1 0
X 0 Q0 Q0’
D C Q Q’
Positive edge triggered

19. °2/17/2020
° Consider two latches combined together
° Only one C value active at a time
° Output changes on falling edge of the clock

20. °2/17/2020
D gets latched to Q on the rising edge of the clock.
° Stores a value on the positive edge of C
° Input changes at other times have no effect on
output
C
D Q
Q’
0 0 1
1 1 0
X 0 Q0 Q0’
D C Q Q’
Positive edge triggered

21. °2/17/2020
° Stores a value on the positive edge of C
° Input changes at other times have no effect on
output

22. Positive Edge-Triggered J-K Flip-Flop
0 0 Q0 Q0’
0 1 0 1
1 0 1 0
1 1 TOGGLE
QJ Q’CLKK°Created from D flop
°J sets
°K resets
°J=K=1 -> invert output
°2/17/2020

23. °2/17/2020
° Two data inputs, J and K
° J -> set, K -> reset, if J=K=1 then toggle output
Characteristic Table

24. 2. Positive Edge-Triggered T Flip-Flop
0 Q0 Q0’
1 TOGGLE
Q Q’CT
°Created from D flop
°T=0 -> keep current
°K resets
°T=1 -> invert current
°2/17/2020

25. °2/17/2020
• J, K are synchronous inputs
o Effects on the output are synchronized with the CLK input.
• Asynchronous inputs operate independently of the synchronous
inputs and clock
o Set the FF to 1/0 states at any time.

26. °2/17/2020

27. °2/17/2020
° Flip flops store outputs from combinational logic
° Multiple flops can store a collection of data

28.  Flip flops are powerful storage elements
◦ They can be constructed from gates and latches!
 D flip flop is simplest and most widely used
 Asynchronous inputs allow for clearing and
presetting the flip flop output
 Multiple flops allow for data storage
◦ The basis of computer memory!
 Combine storage and logic to make a
computation circuit
 Next time: Analyzing sequential circuits.
°2/17/2020

29.  Gunakan Multisim untuk merancang
rangkaian penyimpan 3 bit data secara
paralel.
 Kemudian data tersebut dihapus
 Diisi lagi dengan data baru
°2/17/2020