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Friday, August 16, 2013

PPT On Sequential Circuit And Tabulation Method


Sequential Circuit And Tabulation Method Presentation Transcript:
 1.Sequential Circuit & Tabulation Method

2.Sequential logic contains the logic gates whose output at any instant of time depends upon the present input and also the previous inputs.
Memory elements are required in sequential circuits.
 It consists of combinational circuits to which memory elements are connected to form a feedback path.

These are the devices capable of restoring binary information within them.
The binary info stored in memory elements at any given time defines the state of sequential circuit.
The sequential circuit receives binary information from external inputs. These inputs together with the present state of memory elements determine the binary value at output terminals.

4.There are too many types of sequential circuits. There classification depends and the timing of their signal.
Synchronous Sequential
Asynchronous sequential circuit is a system whose behavior can be defined from the knowledge of its signal and its discrete signal of its time.

5.Asynchronous Sequential:
The behavior of asynchronous depends upon the order in which its input signal change and can be effected at any instant of time.
An asynchronous sequential circuit may be regarded as a combinational circuit with feed back path.

Synchronization is achieved by timing device called master clock generator which generates a periodic train of clock pulses.

Synchronous sequential circuits that use clock pulses in the inputs of the memory elements are called clock sequential circuit. The memory elements used in clocked sequential circuits are called flip-flops.

These circuits are binary cells capable of storing 1 bit information. A flip-flop circuit has two outputs; one for normal value and one for complement value of the bits stored in it.
A flip-flop circuit can be constructed from two NAND gates or two NOR gates. Each circuit forms a basic flip-flop. The cross coupled connection from the output of one gate to the input of the other gate constitutes a feedback path for this reason the circuits are classified as asynchronous sequential circuits.

8.NAND implementation of Flip Flops

9.Tabulation Method
Also known as Quine McCluskey
It is functionally identical to K-map.
There are 4 steps of this method
Step 1:
Write all the given numbers in form of table

10.Step 2
Write their binary equivalent in next column and make groups according to the number of 1’s in the minterm and mark tick

11.Check the binary equivalents for 1 bit change . if a 1 bit change occurs then write the binary number with (-) in column of step 3.
One bit difference implies adjacent
Repeat until nothing left.

12.Again check the binary equivalent for 1 bit change including (-) and mark tick in front of the values whose 1 bit is changed only.
One bit difference implies adjacent.
These are the prime implicants.
Repeat until nothing left.
Then find the expression

13.For Finding Expression
First check for the unmarked number in Step 3 and write the expression of that unmarked value then write the expression of step 4.

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