IP University Paper of Digital Ciruit System-I

Books For Preparation Q1
( a )
How are hazards avoided using SR latches.
2

( b )
Distinguish between Mealy model and Moore model. 1 
( c ) A sequential circuit has two JK flip flops A and B, on input y, and one output y. The J and K inputs are defined as:
Ja = B, Kz = B', Jb = Kb = (xA' + x'A)'
y = ((x'A + xA')B' + (xA' + x'A)'B)

Derive the state table.
3 
( d ) What are cycles in asynchronous circuits. Give examples. 2 
( e ) Assign output values to the dont care conditions in the following flow tale: 00 01 11 10 
A D,- A,0 A,0 B,- 
B B,1 B,1 C,- B,1 
C B,- C,1 C,1 D,- 
D D,0 D,0 A,- D,0 
2 


Q2
( a )
A sequential network has one input (X) and one output (Z). The network examines groups of four consecutive inputs and produces an output Z=1 if the input sequence 0101 or 1001 occurs. The network resets after every four inputs. Determine the mealy state graph and state table.
6

( b )
Draw an ASM chart that specifies a conditional operator to increment register R during state T1 and transfer to state T2 if control inputs z and y are equal to 1 and 0 respectively.
4 


Q3
( a )
Determine the state table corresponding to the following state diagram:

3

( b )
Design an asynchronous sequential circuit with two inputs x1 and x2 and one output z. initially both inputs and outputs are equal to 0. When x1 or x2 becomes 1, z becomes 1. When the second input also becomes 1, the output becomes 0. The output stays at 0 until the circuit foes back to the initial state.
Obtain the primitive flow table and show that it can be reduced to the following flow table:
00 01 11 10 
A A,0 A,1 B,- A,1 
B A,- B,0 B,0 B,0 

Design the circuit using SR latches. 



Q4
( a )
USE IMPLICATION TABLE TO REDUCE THE FOLLOWING TABLE TO A MINIMUM NUMBER OF STATES:
PRESENT STATE NEXT STATE OUTPUT 
X=0 X=1 Z 
A F D 0 
B D A 1 
C H B 0 
D B C 1 
E G B 0 
F A H 0 
G E C 0 
H C F 0 
3

( b )
The state diagram of a control unit is as shown below. It has four states and two inputs x and y.


Draw the equivalent ASM chart 
Design the control unit using D flip flops and decoders. 

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