Page 261 - Programmable Logic Controllers, Fifth Edition - Mobile version

L1 Input Ladder logic program Output L2
CPT ADD SUB MUL DIV MOD SQR
FRD Compare Compute/Math Move/LogicalFile/Misc.
From BCD
1
Source I:012
2 I:012 O:013
3 MOD
Destination B3:0
Thumbwheel 60 LED Modulo
switch Display Source A Thumb_Value
MUL 7
0 6 0 MULTIPLY 14 0 Source B 2
Source A B3:0
60 Dest Actual_Value
Celsius Fahrenheit
Source B 9 1
Destination N7:0
540 Figure 11-15 ControlLogix Modulo (MOD) instruction.
DIV
DIVIDE Thumb_Value = 7
Source A N7:0
540 7
Source B 5 =1
2
Destination N7:1
108
11.6 Other Word-Level Math
ADD Instructions
ADD
Source A N7:1
108 The program of Figure 11-16 is an example of the square
Source B 32
root (SQR) instruction. The operation of the logic rung
Destination B3:1 can be summarized as follows:
140
TOD • When input switch SW is closed the SQR instruc-
TO BCD tion is executed.
Source B3:1 • The number whose square root we want to deter-
140 mine (144) is placed in the source.
Destination O:013 • The function calculates the square root and places it
(12) in the destination.
Figure 11-14 Program for converting Celsius temperature • If the value of the source is negative, the instruction
to Fahrenheit. will store the square root of the absolute (positive)
value of the source at the destination.
• The DIV instruction divides 5 into the 540 and
stores the answer (108) in address N7:1. The program of Figure 11-17 is an example of the ne-
• The ADD instruction adds 32 to the value of 108 gate (NEG) instruction. This math function changes the
sign of the source value from positive to negative. The
and stores the sum (140) in address B3:1. operation of the logic rung can be summarized as follows:
• Finally the TOD instruction is used to convert BCD
values into integers. to interface with the LED display. • When input switch SW is closed the NEG instruc-
• Thus 60°C is displayed as 140°F. tion is executed.
The Modulo (MOD) instruction, shown in Figure 11-15, Input Ladder logic program
is part of the ControlLogix Compute/Math instruction set. L1
This instruction is used to calculate the remainder after the SW SQR
value stored in Source A is divided by the value stored in SW SQUARE ROOT
Source B. In this unconditional rung example: Source A N7:101
144
Destination N7:105
Source A 12
Source B = Dest (remainder)
( 144 = 12)
Thumb_Value = Actual_Value
2 Figure 11-16 SLC 500 SQR (square root) instruction.

242 Chapter 11 Math Instructions

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