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What will be the minimum size of ROM which maintains truth table of square of 3 bit numbers(in bits) ?
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2 Answers

8 votes
8 votes
Best answer

Truth Table will be as:

Input (Address lines) Output (Data)
I0 I1 I2 B0 B1 B2 B3 B4 B5
0 0 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 1
0 1 0 0 0 0 1 0 0
0 1 1 0 0 1 0 0 1
1 0 0 0 1 0 0 0 0
1 0 1 0 1 1 0 0 1
1 1 0 1 0 0 1 0 0
1 1 1 1 1 0 0 0 1

example for 111 (7), square will 110001 (49)

so it will have 3 address line  mean 8 address [000 to 111] and 6 bits [B0 to B5] at each address = 8 X 6 = 48 bits 

but we do not need to store B4 and B5 [as B4 = 0 and B5 = I2 ]

so ROM will be of size 8 x 4 = 32bits.

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4 Comments

We store those 8 rows in ROM. Now to select any one of them we need 3 address lines- which are I0, I1 and I2- they need not be stored.
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Thanks got it.
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@arjun sir , why did u say that 0, I1 and I2- they need not be stored ?
I didn't Understand why are you skipping this ?
Please make it simple
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2 votes
2 votes
no is 3 bit long.. square of 3 bit no is 6 bit long..
total 8 nos (0 to 7) which truth table has to store..
total size is 8*6=48 bit