Title: Flip-flop and Finite State Machine
1Flip-flop and Finite State Machine
- By
- Radha Iyer
- Prof Dr. Sin-Min Lee
- CS147 Computer Organization and Architecture
2What is Sequential Circuits?
- A Sequential Circuit can be defined as circuit
- having sequential logic. Sequential logic is a
type - of a logic circuit whose output depends not only
on - current inputs but also on previous inputs.
3What are flip-flops?
- In order to remember previous inputs, sequential
circuits must have some sort of storage element.
This storage element is called flip-flop. - Flip-flop depends on previous inputs to the
circuit. - The basic memory unit is called an SR flip-flop.
- We can describe flip-flops using characteristic
table.
4SR Flip-Flop operation (BUILT WITH NOR GATES) 6 SR Flip-Flop operation (BUILT WITH NOR GATES) 6 SR Flip-Flop operation (BUILT WITH NOR GATES) 6 SR Flip-Flop operation (BUILT WITH NOR GATES) 6 SR Flip-Flop operation (BUILT WITH NOR GATES) 6 SR Flip-Flop operation (BUILT WITH NOR GATES) 6 SR Flip-Flop operation (BUILT WITH NOR GATES) 6 SR Flip-Flop operation (BUILT WITH NOR GATES) 6
Characteristic table Characteristic table Characteristic table Excitation table Excitation table Excitation table Excitation table Excitation table
S R Action Q(t) Q(t1) S R Action
0 0 Keep state 0 0 0 X No change
0 1 Q 0 0 1 1 0 reset
1 0 Q 1 1 0 0 1 set
1 1 Unstable combination 1 1 X 0 race condition
5Unstable Circuit
- S-stands for set
- R- stands for re-set
- If both S and R are set to1 in the SR flip-flop
at the same time then it resulted in an unstable
circuit, so this combination is not allowed. - To take care of this problem JK flip-flops were
developed.
6What is JK flip-flop?
- It is a variation to SR flip-flop, but it takes
care of the SR1 combination. - (JSet, KReset)
- When it comes to the SR1 it toggles. It is a
great improvement over the SR flip-flops.
7JK Flip Flop operation 6 JK Flip Flop operation 6 JK Flip Flop operation 6 JK Flip Flop operation 6 JK Flip Flop operation 6 JK Flip Flop operation 6 JK Flip Flop operation 6 JK Flip Flop operation 6 JK Flip Flop operation 6
Characteristic table Characteristic table Characteristic table Characteristic table Excitation table Excitation table Excitation table Excitation table Excitation table
J K Qnext Comment Q Qnext J K Comment
0 0 hold state 0 0 0 X No change
0 1 reset 0 1 1 X Set
1 0 set 1 0 X 1 Reset
1 1 toggle 1 1 X 0 No change
8What are D flip-flops?
- Another modified version of SR flip-flops are D
flip-flops. - D stands for data flip-flops.
- It represents physical computer memory.
- The output always takes on the state of the D
input at the rising clock edge. - D flip-flops are very useful as they capture the
signal when the clock rises. - Flip-flops are very useful and are found in a lot
of electronic devices.
9Truth table
Clock D Q Qprev
Rising edge 0 0 X
Rising edge 1 1 X
Non-Rising X Qprev
10Finite State Machine
- It is a model of behavior composed of a finite
number of states, transitions between those
states, and actions, (wikipedia,2000). - A finite state machine is an abstract model of a
machine with a primitive internal memory. - It depicts the graphical part of the flip-flops.
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12Moore/Mealy Machines
- Moore machine represents the JK flip-flops
- Output depends only on the state.
- Example for the Moore machine model will be the
elevator door, which just opens and closes - Mealy Machine depends on output and state.
- Example of Mealy Machine will be Microwave oven.
13Mealy Machine for JK flip-flops
14Conclusion
- We learned about flip-flops which are basic
storage elements. - There were different kinds of flip-flops versions
developed SR, JK, D flip-flops. - Then we learned about Finite State Machines which
are primitive internal memory. - We saw Moore Machine, Mealy Machine which are
types of Finite State machines.
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16Sources
- http//en.wikipedia.org/wiki/Flip-flop_(electronic
s) - http//en.wikipedia.org/wiki/Finite-state_machine