# add and sub bcd to seven segment

Discussion in 'The Projects Forum' started by mohsen, Oct 23, 2010.

1. ### mohsen Thread Starter Active Member

Oct 24, 2008
37
0
i'm trying to do the add/ sub for my project
i know how to do add but don't really know how to implement sub to it

also, when i tried to test the add the display is always on i tried to change in input but i alway get the 7 segment on

thanks

File size:
35.5 KB
Views:
18
File size:
41.6 KB
Views:
18
2. ### tom66 Senior Member

May 9, 2009
2,613
214
You have not specified what number system you are using. If you are not dealing with negative numbers then this is not important.

To take away a number you complement (invert) the bits and add 1 to this.

3. ### mohsen Thread Starter Active Member

Oct 24, 2008
37
0
well i finally found out how to do the subtraction,
but i left with the negative number how can i solve it
let's say i subtract 2 from 4
2 - 4 = -2
how can i make it -2
otherwise my circuit work fine

4. ### AlexR Well-Known Member

Jan 16, 2008
735
54
To subtract 2 from 4 you would change the 2 to -2 and then add.
4 + (-2) = 2
Code ( (Unknown Language)):
1.
2. 4 = 0100
3. 2 = 0010
4.
5. -2 = (1101 + 0001) = 1110
6.
7. 4 + (-2) =  0100
8.             1110
9.          =  0010 = 2

5. ### mohsen Thread Starter Active Member

Oct 24, 2008
37
0
well it's not quit what i need.
in this case i will end up with 2 instead of -2 ans so on