Logix5000 Controllers General Instructions - SLAC Confluence

Timer and Counter Instructions (TON, TOF, RTO, TONR, TOFR, RTOR, CTU, CTD, CTUD, RES) 129Execution:Conditionprescanrung-condition-in is falseRelay Ladder ActionThe .CD bit is set to prevent invalid decrements during the first program scan.The rung-condition-out is set to false.The .CD bit is cleared.The rung-condition-out is set to false.rung-condition-in is trueexamine .CD bit.CD bit = 0.CD bit is set.ACC = .ACC - 1.ACC valuerolls overyes.CD bit = 1no.OV bit is cleared.DN bit is cleared.OV bit = 1examine .OV bit.OV bit = 0examine .UN bit.UN bit = 0examine .OV bit.OV bit = 0.UN bit = 1.OV bit = 1.UN bit is setexamine .ACC.ACC ≥ .PRE.ACC < .PRE.DN bit is cleared.DN bit is setrung-condition-out is set totrueendpostscanThe rung-condition-out is set to false.Publication 1756-RM003I-EN-P - January 2007