Rockwell Automation 1771-QB Linear Pos. - Manual (Page 219)

Data Formats
Appendix H
HĆ2
Following are two methods to get the negative of a number using the 2’s
complement method.
Bit Inversion Method
To get the 2’s complement of a number using the bit inversion method you must
invert each bit from right to left after the first 1.
Example: To represent -1524 (decimal) in 16-bit 2’s complement format, we
start with the binary equivalent of the positive of the number.
1524 (decimal) = 0000 0101 1111 0100 (Binary)
Next, we invert all the bits of the number from right to left starting with the bit
after the first 1 that we encounter.
-1524 (decimal) = 1111 1010 0000 1100
Subtraction Method
To get the 16-bit 2’s complement of a number using the subtraction method you
must subtract the number from 2
16 .
Thus to represent -1524 (decimal):
1 0000 0000 0000 0000
-0000 0101 1111 0100
____________________
1111 1010 0000 1100
Many of the words in the module’s data blocks use implied decimal points. This
means that, although the value you want to enter into a word may have a
fractional component, you only enter the digits, not the decimal point, when you
type it into the programmable controller data table.
Implied Decimal