# what can i do if i want that the displays show a negaive number in a 7 segment displays?

#### Sebastián Gómez 1

Joined Dec 5, 2016
6
i 'm making a circuit of Adder/Substractor in 1's complement, the objective is put the answer in 7 segment displays. I have at least the 75% of the circuit made, how you can see in the attached image, the only problen that I have is that in the output (7 segments displays) doesn't show the negative numbers. For example, if i have 1-2=-1, that means that in binary will be S(1) M(0001) -> (10001). the circuit literally do the binary number, i mean, instead of show -1 (1 0001) it shows 17 (10001) what can i do if i want that the displays show -1?

#### crutschow

Joined Mar 14, 2008
25,269
You can use the middle segment of an additional 7-segment display as a minus sign.

#### Sebastián Gómez 1

Joined Dec 5, 2016
6
You can use the middle segment of an additional 7-segment display as a minus sign.
in that case i could use a third 7 segment, but i dont know how to pull apart the sign from the magnitude, thats the real problem.

#### WBahn

Joined Mar 31, 2012
26,074
If you are doing 1's complement, you need to first define what the width is since all of the binary representations that deal with negative numbers are fixed width.

It sounds like you have a 5-bit representation. If so, how do you know if the value is positive or negative? If it's negative, then how do you determine the positive value that should be displayed?

Try to answer these questions based on the definition of 1's complement. If you can, then how to manipulate them should be pretty straightforward.