550 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 15 Advanced Math Instructions (LN, LOG, XPY)
Description: The Source must be greater than zero, otherwise the overflow status bit (S:V) is
set. The resulting Destination is greater than or equal to -37.92978 and
less than or equal to 38.53184.
Arithmetic Status Flags: Arithmetic status flags are affected.
Fault Conditions: None
Execution:
Relay Ladder
Function Block
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 The controller calculates the log of the Source and places the result in the Destination.
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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