i want to make 4-bit Arithematics Logic Unit (ALU)
don't use any full IC (using logic gates only)
I want idea for this design please
***************************************************************
4 bit ALU able to generate the following four flag (i want to know what the meaning of flag):
a-carry/borrow flag to be set on carry (addition) or borrow (subtraction) operations
b-sign flag to be set when the resulting number is negative (2's complement only)
c-zero flag to be set if the resulting number is zero
d-overflow flag to be set if the two most significant carry outputs are not equal
i need help plz!!!!!

 

If I am not wrong, if you know the number of inputs & outputs, you should be able to do it with flip flops.
Just applying the principles of digital electronics.

 

Hello,

The links on this page will give you some ideas:
Arithmetic circuits

Bertus

 

Hello ahmed Elaraby

An ALU requires:
4-BIT's to say what function to execute.
4-BIT's to the operand "A".
4-BIT's to the operand "B".
4-BIT's to show the function result.

You say: (i want to know what The Meaning of flag):
Flag is a sign: audible, visual, sensory announcing an event which must be notified.
Audible buzzer.
Visual: LED.
Sensitive: a tap on the shoulder.

In the case of ALU is
A BIT to indicate the carry / borrow.
A BIT for displaying the sign.
A BIT to indicate zero.
A BIT to signal the overflow.

Over here there's someone else asking for help about the ALU. Visit this link:
http://forum.allaboutcircuits.com/showthread.php?p=378078 # post378078

regards
at your service