Chapter 4. Ladder Diagram (LD) ProgrammingGFK-2950C February 2018 1354.7.2 Down CounterThe Down Counter (DNCTR) function counts down from a preset value. The minimumPreset Value (PV) is zero; the maximum PV is +32,767 counts. When the Current Value(CV) reaches the minimum value, -32,768, it stays there until reset. When DNCTR is reset,CV is set to PV. When the power flow input transitions from OFF to ON, CV isdecremented by one. The output is ON whenever CV 0.The output state of DNCTR is retentive on power failure; no automatic initialization occursat power-up.WarningDo not use the Address of the down counter with otherinstructions. Overlapping references cause erraticcounter operation.Note: For DNCTR to function properly, you must provide an initial reset to set the CV to the value inPV. If DNCTR is not initially reset, CV will decrement from 0 and the output of DNCTR will beset to ON immediately.OperandsParameter Description Allowed Operands OptionalAddress(????)The beginning address of a three-word WORD array:Word 1: Current Value (CV)Word 2: Preset Value (PV)%Word 3: Control wordR, W, P, L, symbolic NoR When R receives power flow, it resets the counter's CV to PV. Power flow NoPV Preset Value to copy into word 2 of the counter's addresswhen the counter is enabled or reset. 0 PV 32,767. If PV isout of range, word 2 cannot be reset.All except S, SA, SB, SC NoCV The current value of the counter All except S, SA, SB, SCand constantNoExample – Down CounterDNCTR counts 5000 new parts before energizing output %Q00005.
