34 votes

The literal count of a Boolean expression is the sum of the number of times each literal appears in the expression. For example, the literal count of $\left(xy+xz'\right)$ is $4.$ What are the minimum possible literal counts of the product-of-sum and sum-of-product representations respectively of the function given by the following Karnaugh map? Here, $X$ denotes "don't care"

- $(11, 9)$
- $(9, 13)$
- $(9, 10)$
- $(11,11)$

5

I am getting 8 literals for SOP, top right most corner '1' can form a group of 4 with corners don't cares and remaining 1's forms a group of 2 so there are total of 2+3+3 literals for SOP. but answer given as (9,10).

10

this is what i have done, plz tell me where i was wrong.

pink ink is for SOP = 2 + 3 + 3 = 8

blue ink is for POS = 2 + 2 + 2 + 3 = 9

0

Can we use the DONT CARE once included angain for grouping ? Here d15 and d8 are grouped twice ? Is this possibe ?

–1

if dont care has been used in pos than can't be used in sop .

since if we used don't care for pos that meas we are considering don't care as 0's ..

since if we used don't care for pos that meas we are considering don't care as 0's ..

2

@gabbar sir

"if dont care has been used in pos than can't be used in sop ." This statement creating so much confusions. Do you have any standard books or any proofs justifying the statement .

AFAIK There is no such restrictions for dont care . Like if we are using one in POS we can use the same for SOP

"if dont care has been used in pos than can't be used in sop ." This statement creating so much confusions. Do you have any standard books or any proofs justifying the statement .

AFAIK There is no such restrictions for dont care . Like if we are using one in POS we can use the same for SOP

61 votes

Best answer

We will be getting two different grouping..

Grouping $1: (9,8)$

GROUPING $2: (9,10)$

Both the grouping are correct representation of the function $f(wxyz)$

PS: Some wrong beliefs about don't cares

- "once you have assumed a don't care as '1' u can't use the same don't care for grouping zeros and vice versa"
- "if don't care has been used in POS than can't be used in SOP"

Both these statements are wrong. Don't care simply means just don't care -- say we use don't care $d3$ for grouping $1$ in SOP we can use $d3$ for grouping 0 in POS. (The literals in SOP and POS may not be the same)

K-Map grouping is not unique. And the question says about minimal literals. So, the **best answer would be (9,8) **Since there is no option in GATE we can go with $(9,10)$ (the question setter might have missed Grouping 1)

5 votes

3

**once you have assumed a don't care as '1' u can't use the same don't care for grouping zeros and vice versa.**

1

@arjun Sir is this statement true ?

"once you have assumed a don't care as '1' u can't use the same don't care for grouping zeros and vice versa"

"once you have assumed a don't care as '1' u can't use the same don't care for grouping zeros and vice versa"

6

No same don't care can be used both in SOP and POS . Moreover , minimum number of literals is not necessarilly unique.Hence we can go for option c since (9,8) is not in the options.For reference Chapter 3 "implification of boolean function" - Digital Logic and Computer Design by Morris Mano

0

both are different function we can can use same dont care for both sop and pos .

@Bikram sir verify this pls

@Bikram sir verify this pls

0

@Arjun sir

If these questions come so should we answer

1)the best nearest answer

2)or should we refrain from answering such questions?

3)and also one more point, are marks awarded to all in such a situation or not?

Please help. All seniors please help us in this muddle.. It would be a great help:)

If these questions come so should we answer

1)the best nearest answer

2)or should we refrain from answering such questions?

3)and also one more point, are marks awarded to all in such a situation or not?

Please help. All seniors please help us in this muddle.. It would be a great help:)

5 votes

0

@Pooja Palod We can write SOP using 8 literal as well:

**y'w'+xyz'+x'z'w ** which is minimal and even in question it is mentioned that "What are the **minimum** possible literal counts of the product-of-sum and sum-of-product representations".

so, Answer should be (9,8) as it is minimum possible.

@Arjun Sir please look this question.

Correct me if I am wrong.