Chapter 4. Ladder Diagram (LD) Programming106 PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual GFK-2950C4.5.2 Edge DetectorsFalling Edge Trigger Rising Edge TriggerThese function blocks detect the changing state of a Boolean signal and produce a single pulse whenan edge is detected.When transitional instructions, such as Transition Coils or Transition Contacts, are used inside afunction block, there is a problem when the same function block is called more than once per scan.The first call executes the transition correctly but subsequent calls do not because they see the stateas adjusted from the first call. The rising and falling edge trigger instructions solve this problem.These instructions have their own instance data that can be a member or an input of the functionblock so that the transition state follows that of the function block instance and not the functionblock.If an edge detector function block is used within a UDFB, its instance data must be a membervariable of the UDFB.OperandsParameter Description Allowed Operands Optional???? Instance data for function block. This is astructure variable, described below.F_TRIG, R_TRIG NoCLK Input to be monitored for a change in state. All YesQ Edge detection output. Must be flow in LD. In other languages alltypes allowed except S, SA, SB, SC andconstants.YesInstance Data StructureThese elements cannot be published or written to.Element Name Type DescriptionCLK BOOL Edge detection input. Not accessible in user logic.Q BOOL Edge detection output. Accessible in user logic. Read only.STATE BOOL Internal value. Not accessible in user logic.ENO BOOL Enable Output. User logic can access as read-only.
