Omron GRT1 - 27-11-2006 Operation Manual page 93

PROFIBUS Technology
A-6 Protection Mechanisms
PROFIBUS DP provides protection functions against parameterization errors or failure of the transmission
equipment. Time monitoring is provided both at the master and the slave devices. The monitoring interval is
specified when the system is configured.
The PROFIBUS DP Master monitors data transmission of each individual slave device with the Data-Control-
Timer. This timer expires if response data is not correctly received from the slave within the monitoring interval.
If the automatic error reaction (Auto-CLEAR) has been enabled, the PROFIBUS DP master exits its OPERATE
state, switches the outputs of all assigned slaves to the fail-safe status and changes to the CLEAR state.
Slave devices use a watchdog to detect failures of the master or the bus. If no data exchange with the master
occurs within the set watchdog time interval, the slave automatically switches its outputs to the fail-safe mode.
Also, access protection is provided for the inputs and outputs of the slaves operating in multi-master systems.
Only authorized masters can access their slaves.
A-7 Network Operation Modes
PROFIBUS DP distinguishes four different network operation modes:
• OFFLINE: Communication with all PROFIBUS DP participants (masters and slaves) is stopped. The Mas-
ter ceases to access the PROFIBUS network.
• STOP: Communication between the master and its slaves is stopped. Only communication between the
master and other masters is possible.
• CLEAR: The master tries to set parameters, check the configuration, and perform data exchange with its
associated slaves. Data exchange involves reading the inputs of the PROFIBUS DP slaves and writing
zeros to the outputs of the slaves.
• OPERATE: The master exchanges I/O data with its assigned slaves. Also, the master cyclically sends its
own status to all assigned PROFIBUS DP slaves using a broadcast message.
The PROFIBUS DP Master Unit will always be in one of these four modes. Mode transitions will be performed
via intermediate modes. For example, a mode transition from OFF-LINE to OPERATE, will be performed as
→ →
OFF-LINE STOP CLEAR
If an error occurs during the data exchange phase of the master, the 'Auto-CLEAR' function determines the
subsequent actions. If this function has been disabled, the master remains in the OPERATE mode. If the func-
tion has been enabled, the master automatically changes the network to the CLEAR mode, in which the out-
puts of the assigned PROFIBUS DP slaves are switched to zero, i.e. the 'fail-safe' state. The master continues
to read the inputs of the slaves.
A-8 Configuring the PROFIBUS DP Master
In order to operate a PROFIBUS network, each master in the network needs to be configured. This process of
PROFIBUS master configuration involves
• setting up the network topology, i.e. assigning the slave devices to the master device,
• defining the parameterization data, which the master will send to each of the slave devices, before process
data exchange can commence
• defining the configuration data, i.e. defining the process data, which will be exchanged,
• setting up the bus parameters, which define the baud rate and the bus timing parameters.
• downloading the configuration setup to the master device.
The configuration process is usually facilitated by a special Computer based program, often referred to as a
configurator. The configurator requires special configuration files, defining the configuration options for each
device, which is to participate in data exchange. The files must be provided by the manufacturer of the device.
Two types of configuration technology exist:
• Configuration technology based on FDT/DTM technology
• Configuration technology based on GSD-files
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OPERATE.
Appendix A