Bit flag for the first program cycle

Question:
Many PLC have a system flag presenting the first run of the user program via a TRUE level. For all the following program cycles this flag is set to FALSE level. These system flags are used in order to initialise function block inputs with certain values during the first user program run.

How can such a first-cycle system flag be realised in case of the 'classic' 9300 servo controllers?

Answer:

• Assign a TRANSx function block to the input with the signal FIXED 1.
• Set the edge evaluation to 'rising edge' and the pulse duration to 0.001 s (= 1 ms = 1 program cycle).
• Set the TRANSx function block to the first position of the processing list C0465/x.

The output of the TRANSx element is set to TRUE level for the first program cycle. Consequently, it can be used for user initialisation (e. g. precharge of an integrator with the absolute value of the feedback system).