Automating Manufacturing Systems - Process Control and ...

plc numbers - 13.7
Type
unsigned
signed
2s compliment
Description
binary numbers can only have positive values.
the most significant bit (MSB) of the binary number
is used to indicate positive/negative.
negative numbers are represented by complimenting
the binary number and then adding 1.
Range for Byte
0 to 255
-127 to 127
-128 to 127
Figure 13.9
Binary (Integer) Number Types
Examples of signed binary numbers are shown in Figure 13.10. These numbers use
the most significant bit to indicate when a number is negative.
decimal
binary byte
2
1
0
-0
-1
00000010
00000001
00000000
10000000
10000001
-2 10000010
Note: there are two zeros
Figure 13.10
Signed Binary Numbers
An example of 2s compliment numbers are shown in Figure 13.11. Basically, if the
number is positive, it will be a regular binary number. If the number is to be negative, we
start the positive number, compliment it (reverse all the bits), then add 1. Basically when
these numbers are negative, then the most significant bit is set. To convert from a negative
2s compliment number, subtract 1, and then invert the number.