P3: Basic Plc Program For Sinumerik 840D Sl; Brief Description - Siemens SINUMERIK 840D sl Function Manual

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
● Event-driven signal exchange
● Messages
Cyclic signal exchange
The cyclically-exchanged signals consist primarily of bit arrays.
● They contain commands transferred 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 acknowledgement-
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 does not
require user acknowledgement, this does not affect NC processing.
Basic Functions
Function Manual, 01/2015, 6FC5397-0BP40-5BA2
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