# 4-bit binary subtractor

## Main Question or Discussion Point

Hello folks :

the task is to design a circuit which subtracts 4 bit binary number a3,a2,a1,a0 and b3...b0. the MSB is a sign bit.

Assume that you are given half-adders and full-adders, i.e. you don't have to design the logic of the half-adder or full adder chip.
the two numbers are fed into the circuit on 2 serial lines and the output is also read out serially.

Please have look at the attachement and Let me know if its Correct!!!

Thanks!!!

electro ;)

#### Attachments

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c'mon jack asses move ur ass and check the ans. atleast!!

or r u all That dumb???

c = a - b (1)
c = a + 2comp(b) (2)
c = a + ~b + 1 (3)

All three equations are equivalent. Surely you can implement equation 3 on your own, especially since you have adders available.
Or are you that dumb?

egsmith said:
c = a - b (1)
c = a + 2comp(b) (2)
c = a + ~b + 1 (3)

All three equations are equivalent. Surely you can implement equation 3 on your own, especially since you have adders available.
Or are you that dumb?

You didn't tell me anything about the "figure" attached I just wanted to know if its OK ?
u

Ouabache
Homework Helper
electro-man said:
Hello folks :

the task is to design a circuit which subtracts 4 bit binary number a3,a2,a1,a0 and b3...b0. the MSB is a sign bit.

Assume that you are given half-adders and full-adders, i.e. you don't have to design the logic of the half-adder or full adder chip.
the two numbers are fed into the circuit on 2 serial lines and the output is also read out serially.

Please have look at the attachement and Let me know if its Correct!!!

Thanks!!!

electro ;)
I believe the reason you haven't gotten many responses is because we're not here to check homework. :zzz: If you had a specific problem that you couldn't figure out, we may be able to steer you in the right direction.

Ouabache said:
I believe the reason you haven't gotten many responses is because we're not here to check homework. :zzz: If you had a specific problem that you couldn't figure out, we may be able to steer you in the right direction.

Or may be u're not "good enough" to see the answer and if wrong, "steer" as you say, in the right direction! :tongue2:

electro-man said:
Or may be u're not "good enough" to see the answer and if wrong, "steer" as you say, in the right direction! :tongue2:
I suggest that you reconsider your approach. There are surely several here who can be of assistance but won't. The people you are dealing with here are adults, and adults don't respond to goading.

KM

electro-man said:
c'mon jack asses move ur ass and check the ans. atleast!!

or r u all That dumb???
You can't be serious? Why would anyone want to help you when you act like this? I sure as hell won't.