Detailed Description
2.7 Structure and functions of the basic program
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
2-37
2.7.1 Start-up and synchronization of NCK PLC
Loading the basic program
The basic program must be loaded with the S7 tool when the PLC is in the Stop state. This
ensures that all blocks in the basic program will be initiated correctly the next time they are
called. An undefined state may otherwise develop on the PLC (e.g., all PLC LEDs flashing).
Start-up
The synchronization of NCK and PLC is performed during start-up. The system and user
data blocks are checked for integrity and the most important basic program parameters are
verified for plausibility. In the event of an error, the basic program outputs an error identifier
to the diagnostic buffer and switches the PLC to STOP.
A warm restart is not provided, i.e., following system initialization, the operating system runs
organization block OB 100 and always commences cyclic execution at the start of OB 1.
Synchronization
The PLC is synchronized with the HMI and NCK and CP during power-up.
Sign-of-life
After a correct initial start and the first complete OB1 cycle (initial setting cycle) the PLC and
NCK continuously exchange sign of life signals. If the sign-of-life signal from the NCK fails to
arrive, the PLC/NCK interface is neutralized and the signal "NCK CPU ready" in DB 10 is set
to zero.
2.7.2 Cyclic operation (OB1)
General
The NCK PLC interface is processed completely in cyclic mode. From a chronological
viewpoint, the basic program runs ahead of the user program. In order to minimize the
execution 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 functions
• M decoding (M00 - M99),
• M, S, F distribution
• Transmission of the MCP signals via the NCK (on the 840D only)
• Acquisition and conditioning of the user errors and operating messages.
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