Cyclic Operation; Monitor/Control Using The Simatic Manager - Siemens SINUMERIK 840Di sl Commissioning Manual

PLC commissioning
6.7 Testing the PLC program
6.7.2

Cyclic operation

In cyclic operation, communication or exchange of data and signals is carried out between
the PLC and the components NC, HMI (e.g. HMI Advanced) and MCP (machine control
panel).
The execution of the PLC program is carried out such that - with regard to time - the basic
PLC user program is executed prior to the PLC user program.
NC communication
Communication of the PLC with the NC is carried out using the NC/PLC interface. The
interface is divided into the following areas:
● Mode groups
● Channels
● Axes/spindles
● General NC data
Data exchange through the NC/PLC interface is carried out in the basic PLC program at the
beginning of "OB1". This ensures that the data for the PLC remain constant over the entire
PLC cycle.
The current G functions of the NC channels are transferred to the PLC (provided function is
activated) at the process alarm level (OB40).
Sign-of-life monitoring
A cyclic, mutual sign-of-life monitoring function is activated between PLC and NCK once
power-up and the first OB1 cycle have been completed.
In case of failure of the PLC or in case of STOP of the PLC program execution, the following
alarm is displayed:
● Alarm "2000 sign-of-life monitoring for PLC"
6.7.3

Monitor/control using the SIMATIC Manager

The SIMATIC Manager provides extensive functionality for testing the PLC program or the
module.
Monitoring and modifying variables
The menu command Target system > Monitor/control variable is used to start the tool
"Monitor/control variable".
The following functions can be performed with "Monitor/Control Variable":
● Monitoring of variables
● Monitoring of variables
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Display of the actual value of individual variables of the PLC user program or of the CPU
module.
Commissioning Manual, 05/2008, 6FC5397–4CP10–4BA0
Manual