Page 393 - Programmable Logic Controllers, Fifth Edition - Mobile version

Part 5 Math, Comparison,

and Move Instructions

Math Instructions Part Objectives

ControlLogix basic math instructions include addition, After completing this part, you will be able to:
subtraction, multiplication, division, and square root.
Figure 15-77 shows the Compute/Math toolbar for the • Utilize ControlLogix math instructions in programs
ControlLogix controller. • Utilize ControlLogix comparison instructions in
The ADD instruction is used to add two numbers. programs
This instruction adds these values from Source A and • Utilize ControlLogix move instructions in programs
Source B. The source can be a constant value or a tag. • Develop and follow the operation of programs that use
The result of the ADD instruction is put in the destination math, comparison, and move instructions
(Dest) tag.
Figure 15-78 shows an example of an ADD instruction
rung along with its Monitor Tags window. The operation
of the rung can be summarized as follows:
• When the Add_Sw is closed the rung will be true.
• The ADD instruction will execute to add the num-
ber from Source A (Value_A) and the value from Input Ladder logic program
Source B (Value_B). Add_Sw
L1
• The result will be stored in the Dest tag <Local:1:I.Data.1> ADD
(Total_Value). Add_Sw Add Value_A
25
• In this example, the 25 was added to 50 and the Source A Value_B
result (75) was stored in Total_Value. Source B 50
Total_Value
The SUB instruction is used to subtract two numbers. Dest 75
Figure 15-79 shows an example of a SUB instruction rung
Tag Name Value Style Data Type
Total_Value 75 Decimal DINT
Value_A 25 Decimal DINT
CPT ADD SUB MUL DIV MODSQR
Value_B 50 Decimal DINT
Add_Sw 1 Decimal BOOL
Compare Compute/Math Move/Logical File/Misc.

Figure 15-77 Compute/Math toolbar for the ControlLogix Figure 15-78 ADD instruction rung and its Monitor Tags
controller. window.

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