Logix5000 Controllers General Instructions - SLAC Confluence

134 Timer and Counter Instructions (TON, TOF, RTO, TONR, TOFR, RTOR, CTU, CTD, CTUD, RES)Execution:Condition Function Block Action Structured Text Actionprescan No initialization required. No initialization required.instruction first scan CUEnable n-1 and CDEnable n-1 are set. CUEnable n-1 and CDEnable n-1 are set.instruction first run CUEnable n-1 and CDEnable n-1 are set. CUEnable n-1 and CDEnable n-1 are set.EnableIn is cleared EnableOut is cleared, the instruction does nothing,and the outputs are not updated.EnableIn is set The instruction sets CUEnable n-1 and CDEnable n-1 .On a cleared to set transition of EnableIn:naThe instruction sets CUEnable n-1 and CDEnable n-1 .EnableIn is always set.• The instruction executes.• EnableOut is set.reset When set, the instruction clears CUEnable n-1 ,CDEnable n-1 , CU, CD, DN, OV, and UN and setsACC = zero.The instruction executes.postscan No action taken. No action taken.When set, the instruction clears CUEnable n-1 ,CDEnable n-1 , CU, CD, DN, OV, and UN and setsACC = zero.Example:When limit_switch1 goes from cleared to set, CUEnable is set for onescan and the CTUD instruction increments the ACC value by 1. WhenACC ≥ PRE, the DN parameter is set, which enables the function blockinstruction following the CTUD instruction.Structured TextCTUD_01.Preset := 500;CTUD_01.Reset := Restart;CTUD_O1.CUEnable := limit_switch1;CTUD(CTUD_01);counter_state := CTUD_01.DN;Function BlockPublication 1756-RM003I-EN-P - January 2007