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Compare Instructions (CMP, EQU, GEQ, GRT, LEQ, LES, LIM, MEQ, NEQ) Chapter 5
Greater Than (GRT)
Operands:
The GRT instruction tests whether Source A is greater than Source B.
IF sourceA > sourceB THEN
<statements>;
Relay Ladder
Operand
Source A
Source B
Type
SINT
INT
DINT
REAL string
SINT
INT
DINT
REAL string
Format
immediate tag
Description
value to test against Source B immediate tag value to test against Source A
•
If you enter a SINT or INT tag, the value converts to a DINT value by sign-extension.
•
String data types are:
–
default STRING data type
–
any new string data type that you create
•
To test the characters of a string, enter a string tag for both Source A and Source B.
Structured Text
Use the greater than sign “>” as an operator within an expression. This expression evaluates whether sourceA is greater than sourceB.
See Appendix C, Structured Text Programming for information on the syntax of expressions within structured text.
Function Block
Operand
GRT tag
Type
FBD_COMPARE
Format
structure
Description
GRT structure
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Chapter 5 Compare Instructions (CMP, EQU, GEQ, GRT, LEQ, LES, LIM, MEQ, NEQ)
FBD_COMPARE Structure
Input Parameter
EnableIn
SourceA
SourceB
Data Type
BOOL
REAL
REAL
Output Parameter
EnableOut
Dest
Data Type
BOOL
BOOL
Description
Enable input. If cleared, the instruction does not execute and outputs are not updated.
Default is set.
Value to test against SourceB.
Valid = any float
Value to test against SourceA.
Valid = any float
Description
The instruction produced a valid result.
Result of the instruction. This is equivalent to rung-condition-out for the relay ladder
GRT instruction.
Description:
The GRT instruction tests whether Source A is greater than Source B.
When you compare strings:
•
The hexadecimal values of the characters determine if one string is less than or greater than another string. For the hex code of a character, see the back cover of this manual.
•
When the two strings are sorted as in a telephone directory, the order of the strings determines which one is greater. s e r e s l e r a t g r e
A
AB
B
ASCII Characters Hex Codes
1ab $31$61$62
1b $31$62 a ab
$41
$41$42
$42
$61
$61$62
AB < B a > B
Arithmetic Status Flags:
not affected
Fault Conditions:
none
220
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Compare Instructions (CMP, EQU, GEQ, GRT, LEQ, LES, LIM, MEQ, NEQ) Chapter 5
Condition
prescan rung-condition-in is false rung-condition-in is true
Execution:
Relay Ladder
Action
The rung-condition-out is set to false.
The rung-condition-out is set to false.
postscan
Condition
prescan instruction first scan instruction first run
EnableIn is cleared
EnableIn is set postscan
Source A
>
Source B yes no rung-condition-out is set to false rung-condition-out is set to true end
The rung-condition-out is set to false.
Function Block
Action
No action taken.
No action taken.
No action taken.
EnableOut is cleared.
The instruction executes.
EnableOut is set.
No action taken.
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Chapter 5 Compare Instructions (CMP, EQU, GEQ, GRT, LEQ, LES, LIM, MEQ, NEQ)
Example:
If value_1 is greater than value_2, set light_1. If value_1 is less than or equal to
value_2, clear light_1.
Relay Ladder
Structured Text
light_1 := (value_1 > value_2);
Function Block
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Publication 1756-RM003K-EN-P - July 2008
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