There will be the condition of overflow if the signs of the numbers are the same and only if the result has the opposite signs. Operands with different signs will never cause overflow. There will be no condition of overflow if the signs of the numbers are the same in subtraction. Overflow occurs when the signs of the numbers are different if and only if the result has the same sign as the subtrahend.
How do we detect when an overflow does occur?
Overflow is a condition when the result of an arithmetic operation is too large to fit into the resultant bit-group. The easy way to detect the overflow is by checking the answer of addition or subtraction. If the answer of adding two negative numbers comes out positive it is one condition of overflow, and if the result of adding two positive numbers comes out as negative then it is another condition of overflow. If the two signed 2’s complement is added, overflow is detected when the result is negative, but the operands were both positive and when the result comes out in positive, but the operands were negative. Generally, overflow will not occur in addition (subtraction), if the operands have different signs.