Interfacing PIC Microcontrollers

Conversion to the 2s complement negative form from the positive number is

achieved by the inverse process:

SUBTRACT 1, THEN INVERT ALL BITS

For example:

Subtract 1 Invert bits

1  0000 0001 → 0000 0000 → 1111 1111  FF  001

63  0011 1111 → 0011 1110 → 1100 0001  C1  063

128  1000 0000 → 0111 1111 → 1000 0000  80  128

255  1111 1111 → 1111 1110 → 0000 0001  01  255

In this way, 2s complement form allows the usual arithmetic operations to be

applied to negative binary numbers with the correct result. 255 is the limit

of the 8-bit 2s complement range, but more bits can be used if necessary.

SUMMARY 5

• Digital information is stored ...