Solved Paper-III On Topic : Solved Paper-III June 2015

Que : 1 . For the 8-bit word 00111001, the check bits stored with it would be 0111.
Suppose when the word is read from memory, the check bits are calculated to be 1101.
What is the data word that was read from memory?


1. 10011001
2. 00011001
3. 00111000
4. 11000110
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Explanation

Explanation .
Given 8 bit word 00111001. encoded in d8=0 d7=0 d6=1 d5=1 d4=1 d3=0 d2=0 d1=1.
parity is calculated as 01111 which are written as p8p4p2p1.
p1=1
p2=1
p4=1
p8=0.
encode the string as
d8 d7 d6 d5 p8 d4 d3 d2 p4 d1 p2 p1.
001101001111.
check bit at other end is 1101.
c1=1
c2=0
c4=1
c8=1.
xor(1101,0111)=1010 . its decimal conversion is 10. so 10th bit is changed.
10th bit is d6. so we flip it. and we get
00011001