#digital logic GATE 2008- IT self doubt

Question

Please refer to this GATE 2008-IT QUESTION- https://gateoverflow.in/3275/gate2008-it-15

My doubt is which of the following is used to decide the value of carry bit-

1, Carry bit=1, only if carry is generated from a₃+b₃ to bit position 4 ( consider- a₇a₆a₅a₄  a₃a₂a₁a₀

                                                                                                                                                                                     b₇b₆b₅b₄   b₃b₂b₁b₀ )

 

2. Carry bit=1, only if carry is generated anywhere while adding two bits.

3. Carry bit=1, only if Carry_out =1

 

Comments

actually carry_out and carry bit are same variables...

remaining are depends upon your example.

Answer 1

In this Question:  A processor that has the carry, overflow and sign flag bits as part of its program status word (PSW) performs addition of the following two 2′s2′s complement numbers 0100110101001101 and 1110100111101001. After the execution of this addition operation, the status of the carry, overflow and sign flags, respectively will be

 

Carry bit is 1 because Carry_out is 1

If carry generated by A₃+B₃ is 1 then auxiliary carry bit is 1  which they dint asked for.

If carry is generated in the middle and not in the MSBs then carry bit is not 1

Comments

@ RishiRajSingh @ abhishekmehta4u

Thank you.

Answer 2

Your third statement is right.