Siemens SINUMERIK 840D sl Function Manual

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Detailed description2.7 Structure and functions of the basic programBasic logic functions: PLC Basic program powerline (P3 pl)Function Manual, 11/2006, 6FC5397-0BP10-2BA0 512.7.2 Startup and synchronization of NCK PLCLoading the basic programThe basic program must be loaded with the S7 tool when the PLC is in the Stop state. Thisensures that all blocks in the basic program will be initiated correctly the next time they arecalled. An undefined state may otherwise develop on the PLC (e.g., all PLC LEDs flashing).StartupThe synchronization of NCK and PLC is performed during startup. The system and user datablocks are checked for integrity and the most important basic program parameters areverified for plausibility. In the event of an error, the basic program outputs an error identifierto the diagnostic buffer and switches the PLC to STOP.A warm restart is not provided, i.e., following system initialization, the operating system runsorganization block OB 100 and always commences cyclic execution at the start of OB 1.SynchronizationThe PLC is synchronized with the HMI and NCK during power up.Sign of lifeAfter a proper initial start and the first complete OB1 cycle (initial setting cycle) the PLC andNCK continuously exchange sign of life signals. If the signoflife signal from the NCK fails toarrive, the PLC/NCK interface is neutralized and the signal "NCK CPU ready" in DB 10 is setto zero.2.7.3 Cyclic operation (OB1)GeneralThe NCK PLC interface is processed completely in cyclic mode. From a chronologicalviewpoint, the basic program runs ahead of the user program. In order to minimize theexecution time of the basic program, only the control/status signals are transmitted cyclically;transfer of the auxiliary functions and G functions only takes place on request.The following functions are performed in the cyclic part of the basic program:• Transmission of the control/status signals• Distribution of the auxiliary and G functions• M decoding (M00 - M99),• M, S, F distribution• Transmission of the machine control panel signals via the NCK (on the 840D only)• Acquisition and conditioning of the user errors and operating messages.