Cyclic Operation (Ob1) - Siemens SINUMERIK 840D sl Function Manual

Synchronization
The PLC is synchronized with the HMI and NCK and CP during powerup.
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 from the NCK fails to
materialize, the PLC/NCK interface is initialized and the signal "NCK CPU ready" in DB10 is
set to FALSE.
13.10.2

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
● Transfer the MCP signals via NCK
● Acquisition and conditioning of the user errors and operating messages.
Control/status signals
A shared feature of the control and status signals is that they are bit fields. The basic program
updates them at the start of OB1.
The signals can be subdivided into the following groups:
● General signals
● Mode group-specific signals (such as mode types)
● Channel-specific signals (such as program and feed modifications)
● Axis- and spindle-specific signals (such as feed disable)
Basic Functions
Function Manual, 01/2015, 6FC5397-0BP40-5BA2
P3: Basic PLC program for SINUMERIK 840D sl
13.10 Structure and functions of the basic program
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