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#1
03-11-2009, 06:24 PM
 hitmen Senior Member Join Date: Sep 2008 Posts: 156
Combinational Logic Circuit to convert Excess 3 code into BCD code

I know that -3 = 0000
-2 = 0001
-1 = 0010
and that 10, 11, 12 are dont care conditions.

But how do I implement the K-map?
#2
03-11-2009, 09:18 PM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

Make a table of the excess 3 codes and their BCD equivalents. Work from that.
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First comes the hardware, then the software.
#3
03-12-2009, 11:37 AM
 hitmen Senior Member Join Date: Sep 2008 Posts: 156

Table ? I dont exactly understand.

-3 = 0000
-2 = 0001
-1 = 0010 (These 3 dont care)

0 = 0011
1 = 0100
2 = 0101
3 = 0110
4 = 0111
5 = 1000
6 = 1001
7 = 1010
8 = 1011
9 = 1100
10 onwards not possible dont care

Where do I go from here?
#4
03-12-2009, 12:48 PM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

Think of your excess 3 codes being applied as select bits to some multiplexers.
__________________
First comes the hardware, then the software.
#5
03-12-2009, 01:19 PM
 vvkannan Senior Member Join Date: Aug 2008 Location: India Posts: 137

Hello hitmen,

Set up a 4 variable k-map . The input variables A,B,C,D are the
excess-3 code bits(starting from 0011 ,which corresponds to A'B'CD) . This is for the first bit of all the output values(which is BCD ).

Similarly do it for the other 3 bits which means you will get 4 K-maps in all
#6
03-12-2009, 03:04 PM
 hitmen Senior Member Join Date: Sep 2008 Posts: 156

Quote:
 Originally Posted by vvkannan Hello hitmen, Set up a 4 variable k-map . The input variables A,B,C,D are the excess-3 code bits(starting from 0011 ,which corresponds to A'B'CD) . This is for the first bit of all the output values(which is BCD ). Similarly do it for the other 3 bits which means you will get 4 K-maps in all
Hi vvkannan,

I understand how to do the question already. But how do the examiners know whether your answer is right or wrong since there are so many dont care conditions? Also, how can a student verify his answer?
#7
03-12-2009, 03:48 PM
 vvkannan Senior Member Join Date: Aug 2008 Location: India Posts: 137

Quote:
 Originally Posted by hitmen But how do the examiners know whether your answer is right or wrong since there are so many dont care conditions? Also, how can a student verify his answer?
First of all i am an undergraduate student and i don't have any experience in correction . I studied this subject last semester.

But yes you are right ,we can have many answers for these type of questions.
We try to get the simplified form which uses the minimum number of gates and incase of dontcares just give them the value which reduces the total number of inputs and gates.
But i think you can have many answers
#8
03-13-2009, 02:53 PM
 hitmen Senior Member Join Date: Sep 2008 Posts: 156

 Tags bcd, circuit, code, combinational, convert, excess, logic

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