Page 90 - Programmable Logic Controllers, Fifth Edition

MOV MVM AND OR XOR NOT CLR

Compare Compute/Math Move/Logical File/Misc

XOR
BITWISE EXCLUS OR
Source A Ι:1.0

Source B Ι:3.0
Destination O:4.0 Rotating cam limit switch

Source A 000000001010101 0
Ι:1.0

Source B 000000001110101 1
Ι:3.0

Destination 000000000100000 1
O:4.0

Figure 4-26 Word-level XOR instruction.
Source: Image Courtesy of Rockwell Automation, Inc.

Any mismatches energize the corresponding bit in word
O:4.0. As you can see, there is a 1 in every bit location in MOV MVM AND OR XOR NOT CLR
the destination corresponding to the bit locations where
Source A and Source B are different, and a 0 in the Compare Compute/Math Move/Logical File/Misc
destination where Source A and Source B are the same.
The XOR is often used in diagnostics, where real-world
inputs, such as rotary cam limit switches, are compared Input A NOT
with their desired states. NOT
Figure 4-27 illustrates the operation of a word-level
NOT instruction. This instruction inverts the bits from the Source B3:9
Destination
B3:10
source word to the destination word. The bit pattern in
B3:10 is the result of the instruction being true and is the Source
inverse of the bit pattern in B3:9. B3:9 0 00000001010101 0
For 32-bit PLCs, such as the Allen-Bradley Control-
Logix controller, the source and destination may be a Destination 1 11111110101010 1
SINT (one-byte integer), INT (two-byte integer), or DINT B3:10
(four-byte integer). Figure 4-27 Word-level NOT operation.

Fundamentals of Logic Chapter 4 71

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