Q. Binary number system using 8 bit registers?

Add 25 and -30 in binary number system using 8 bit registers using:

• Signed magnitude representation
• Signed 1's complement
• Signed 2's complement

Solution:

To do arithmetic addition with one negative number only we should check magnitude of numbers. The number having smaller magnitude is then subtracted from larger number and sign of bigger number is selected. Implementation of such a technique in digital hardware will need a long sequence of control decisions and circuits which will add and compare and subtract numbers. Is there a better substitute than this technique? Let's first try signed 2's complement.

Now let's do addition using signed 2's complement notation:

Please note how easy it is to add 2 numbers employing signed 2's Complement. This method requires just one control decision and just one circuit for adding two numbers however it puts on extra condition that negative numbers must be stored in signed 2's complement notation in registers. This can be obtained by complementing positive number bit by bit and then incrementing resultant by 1 to get signed 2's complement.