Allen-Bradley LOGIX 5000 - Page 375

Select_Limit Instructions
Chapter 4
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018 375
Execution
Function Block
Condition/State Action Taken
Prescan EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is false EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is true EnableIn and EnableOut bits are set to true.
The instruction executes.
Instruction first run N/A
Instruction first scan N/A
Postscan EnableIn and EnableOut bits are cleared to false.
Structured Text
Condition/State Action Taken
Prescan See Prescan in the Function Block table.
Normal Execution See Tag.EnableIn is true in the Function Block table.
Postscan See Postscan in the Function Block table.
Example
The negate_enable input determines whether to negate In or not. The instruction
sets Out = In if NegateEnable is false. The instruction sets Out = -In if
NegateEnable is true.
Function Block
Structured Text
SNEG_01.In := analog_input1;
SNEG_01.NegateEnable := negate_enable;
SNEG(SNEG_01);
output_value := SNEG_01.Out;