Chapter 4. Ladder Diagram (LD) ProgrammingGFK-2950C February 2018 2174.13.2 Timer Function BlocksFunction Function BlockTypeMnemonic DescriptionOff Delay Timer Built-in(instance data isWORD array)See Built-In TimerFunction Blocksbelow.OFDT_HUNDSOFDT_SECOFDT_TENTHSOFDT_THOUSThe Current Value (CV) of the timer resets to zerowhen power flow input is on. CV increments whilepower flow is off. When CV=PV (Preset Value),power flow is no longer passed to the right untilpower flow input is on again.On DelayStopwatchTimerONDTR_HUNDSONDTR_SECONDTR_TENTHSONDTR_THOUSRetentive on delay timer. Increments while itreceives power flow and holds its value whenpower flow stops.On Delay Timer TMR_HUNDSTMR_SECTMR_TENTHSTMR_THOUSSimple on delay timer. Increments while itreceives power flow and resets to zero whenpower flow stops.Timer Off Delay Standard(instance data is astructure variable)See Standard TimerFunction Blocks.TOF When the input IN transitions from ON to OFF,the timer starts timing until a specified period oftime has elapsed, then sets the output Q to OFF.Timer On Delay TON When the input IN transitions from OFF to ON,the timer starts timing until a specified period oftime has elapsed, then sets the output Q to ON.Timer Pulse TP When the input IN transitions from OFF to ON,the timer sets the output Q to ON for a specifiedtime interval.Built-In Timer Function BlocksNote: Special care must be taken when programming timers in program blocks that are not calledevery sweep, and in parameterized blocks and UDFBs. For details, refer to:- Using OFDT, ONDTR and TMR in Program Blocks not Called Every Sweep- Timers that are Skipped by the Jump Instruction- Using OFDT, ONDTR and TMR in Parameterized Blocks, and- Using OFDT, ONDTR and TMR in UDFBs.Data Required for Built-in Timer Function BlocksThe data associated with these functions is retentive through power cycles. Each timer uses a three-word array of %R, %W, %P, %L or symbolic memory to store the following information:Current value (CV) Word 1Preset value (PV) Word 2Control word Word 3
