270 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 6 Compute/Math Instructions (CPT, ADD, SUB, MUL, DIV, MOD, SQR, SQRT, NEG, ABS)
FBD_MATH Structure
Description: The SUB instruction subtracts Source B from Source A and places the result in
the Destination.
Arithmetic Status Flags: Arithmetic status flags are affected.
Fault Conditions: None
Execution:
Relay Ladder
Function Block
Input Parameter Data Type Description
EnableIn BOOL Enable input. If cleared, the instruction does not execute and outputs are not updated.
Default is set.
SourceA REAL Value from which to subtract SourceB.
Valid = any float
SourceB REAL Value to subtract from SourceA.
Valid = any float
Output Parameter Data Type Description
EnableOut BOOL The instruction produced a valid result.
Dest REAL Result of the math instruction. Arithmetic status flags are set for this output.
Condition Action
Prescan The rung-condition-out is set to false.
Rung-condition-in is false The rung-condition-out is set to false.
Rung-condition-in is true Destination = Source B - Source A
The rung-condition-out is set to true.
Postscan The rung-condition-out is set to false.
Condition Action
Prescan No action taken.
Instruction first scan No action taken.
Instruction first run No action taken.
EnableIn is cleared EnableOut is cleared.
EnableIn is set The instruction executes.
EnableOut is set.
Postscan No action taken.
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