Logix5000 Controllers General Instructions - SLAC Confluence

128 Timer and Counter Instructions (TON, TOF, RTO, TONR, TOFR, RTOR, CTU, CTD, CTUD, RES)Description:The CTD instruction is typically used with a CTU instruction thatreferences the same counter structure.When enabled and the .CD bit is cleared, the CTD instructiondecrements the counter by one. When enabled and the .CD bit is set,or when disabled, the CTD instruction retains its .ACC value.rung condition incount-down enable bit (.CD)count-down done bit (.DN)counter accumulated value (.ACC)preset16637The accumulated value continues decrementing, even after the .DNbit is set. To clear the accumulated value, use a RES instruction thatreferences the counter structure or write 0 to the accumulated value.Arithmetic Status Flags:Fault Conditions:not affectednonePublication 1756-RM003I-EN-P - January 2007