Logix5000 Controllers General Instructions - SLAC Confluence

120 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 affectednonePublication 1756-RM003I-EN-P - January 2007