Siemens SINUMERIK 840D sl Function Manual page 991

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Brief description

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) areas. A distinction is made between the following groups for

signals and data:

• Cyclic signal exchange

• Eventdriven signal exchange

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

• 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 that the signals from the NCK remain constant throughout the 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

chaintype magazines).

Data transfer must be as fast and yet as reliable as possible, in order to minimize the effect

on the NC machining process. Data transfer is therefore controlled by alarms and

acknowledgments. 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.

Basic logic functions: PLC Basic program powerline (P3 pl)

Function Manual, 11/2006, 6FC5397-0BP10-2BA0

status information from the NCK (such as program running, interrupted, etc.).

– Mode groups

– Axes/spindles

– General NCK signals

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