Basic Functions
Function Manual 09/2011, 6FC5397-0BP40-2BA0
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13
P3: Basic PLC Program for SINUMERIK 840D sl
13.1 Brief description
General
The PLC basic program organizes the exchange of signals and data between the PLC user program and the
NCK (Numerical Control Kernel), HMI (Human Machine Interface) and MCP (Machine Control Panel). In the case
of signals and data, a distinction is made between the following groups:
• Cyclic signal exchange
• Eventdriven signal exchange
• Messages
Cyclic signal exchange
The cyclically-exchanged signals consist primarily of bit arrays.
• They contain commands transmitted from the PLC to the NCK (such as start or stop) and status information
from the NCK (such as program running, interrupted, etc.).
• The bit fields are organized into signals for:
- Mode group
- Channels
- Axes/spindles
- General NCK signals
The cyclic exchange of data is performed by the basic program at the start of the PLC cycle (OB1). This ensures,
for example, that the signals from the NCK remain constant throughout a cycle.
Event-driven signal exchange NCK → PLC
PLC functions that have to be executed as a function of the workpiece program are triggered by auxiliary
functions in the workpiece program. If a block with auxiliary functions is executed, the type of auxiliary function
determines whether the NCK has to wait for this function to execute (e.g. tool change) or whether the function will
be executed together with the workpiece machining process (e.g. tool loading on milling machines with chain
magazine).
Data transfer must be as fast and yet as reliable as possible, in order to minimize the effect on the NCK
machining process. Data transfer is, therefore, interrupt- and acknowledgment-driven. The basic program
evaluates the signals and data, acknowledges this to the NCK and transfers the data to the application interface
at the start of the cycle. If the data do not require user acknowledgment, this does not affect NC processing.
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