So I'm using this software called logisim and I need to create a decrementer which has two outputs, a sum and a carry out. However, we can only use two gates (each gate can be 8 bit tho). I've spent hours on this and I have no idea. Any help?

 

hi aspect,
Could post a sketch of what you define as a 'gate' and a 'decrementer', showing say 8 bits.

The questions sounds a little odd.
E

 

hi aspect,
Could post a sketch of what you define as a 'gate' and a 'decrementer', showing say 8 bits.

The questions sounds a little odd.
E

Here's the decrementer using the built in components (we cant use it in the final solution).

And an 8-bit NAND gate:

 

hi,
This image shows an 8 Bit NAND Gate.
Also, a decrementer outputs a 'Borrow' bit not a 'Carry'

E

 

hi,
This image shows an 8 Bit NAND Gate.
Also, a decrementer outputs a 'Borrow' bit not a 'Carry'

E

Yea, I meant borrow not carry.

So is there a way to make a decrementer out of two gates?

 

hi aspect,
Sorry to sound picky, but are you sure that you have question correctly stated.

Do you have a copy of the original question as put by your Tutor.?
E

 

hi aspect,
Sorry to sound picky, but are you sure that you have question correctly stated.

Do you have a copy of the original question as put by your Tutor.?
E

Yea:
Build a gate circuit that inputs a number on an 8-bit pin A and decrements
it asserting the result on an 8-bit pin R, and the carry-out on a
pin Cout.
You are allowed only two gate arrays (“gates” in Logisim terminology)
for this exercise. Logisim’s Arithmetic library can not be used.

(A gate array is just an multibit gate)

 

hi,
Look at this example of an 8 Bit parallel Load, Down counter, for one of the 'Gates'

Ask if you have a query.
E