Logix5000 Controllers General Instructions - SLAC Confluence

116 Timer and Counter Instructions (TON, TOF, RTO, TONR, TOFR, RTOR, CTU, CTD, CTUD, RES)After it updates the ACC, the timer sets last_time_scanned =current_time. This gets the timer ready for the next scan.IMPORTANTMake sure to scan the timer at least every 69 minutes while it runs. Otherwise, the ACC valuewon’t be correct.The last_time_scanned value has a range of up to 69 minutes. The timer’s calculationrolls over if you don’t scan the timer within 69 minutes. The ACC value won’t be correct if thishappens.While a timer runs, scan it within 69 minutes if you put it in a:• subroutine• section of code that is between JMP and LBL instructions• sequential function chart (SFC)• event or periodic task• state routine of a phaseArithmetic Status Flags:Fault Conditions:not affectednoneExecution:Condition Function Block Action Structured Text Actionprescan No action taken. No action taken.instruction first scan EN, TT and DN are cleared.EN, TT and DN are cleared.instruction first runEnableIn is clearedEnableIn is setACC value is set to PRE.EN, TT and DN are cleared.ACC value is set to PRE.EnableOut is cleared, the instruction does nothing,and the outputs are not updated.When EnableIn transitions from cleared to set, theinstruction initializes as described for instructionfirst scan.The instruction executes.ACC value is set to PRE.EN, TT and DN are cleared.ACC value is set to PRE.naEnableIn is always set.The instruction executes.resetEnableOut is set.When the Reset input parameter is set, theinstruction clears EN, TT and DN and setsACC = PRE. Note that this is different than using aRES instruction on a TOF instruction.postscan No action taken. No action taken.When the Reset input parameter is set, theinstruction clears EN, TT and DN and setsACC = PRE. Note that this is different than using aRES instruction on a TOF instruction.Publication 1756-RM003I-EN-P - January 2007