How to create a decrementer using only two gate arrays?

Thread Starter

aspect11

Joined Nov 29, 2021
4
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?
 

ericgibbs

Joined Jan 29, 2010
14,648
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
 

Thread Starter

aspect11

Joined Nov 29, 2021
4
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).
Screenshot_1.png
And an 8-bit NAND gate:
Screenshot_2.png
 

ericgibbs

Joined Jan 29, 2010
14,648
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
 

Thread Starter

aspect11

Joined Nov 29, 2021
4
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)
 
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