Siemens SINUMERIK 840Di Function Manual page 1193

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). A distinction is made between the following groups for signals and
data:
• Cyclic signal exchange
• Eventdriven signal exchange
• Messages
Cyclic signal exchange
Signals exchanged cyclically consist primarily of bit fields.
• They contain commands transmitted from the PLC to the NCK (such as start or stop) and
• The bit fields are organized into signals for:
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 the auxiliary functions are used to start
execution of a block, the type of auxiliary function determines whether the NCK has to wait
before executing the function (e.g., during a tool change) or whether the function is executed
in parallel to machining of the workpiece (e.g., for tool preparation on milling machines with
chain-type magazines).
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. Where the data do
not require user acknowledgment, this does not affect NCK machining.
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
status information from the NCK (such as program running, interrupted, etc.).
– Mode groups
– Channels
– Axes/spindles
– General NCK signals
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