Protection Mechanisms; Network Operation Modes - Omron CJ Series Operation Manual

1-1-6

Protection Mechanisms

 Monitoring Time
PROFIBUS DP provides effective 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.
 Monitoring at the Master
The PROFIBUS Master monitors data transmission of the slaves with the Data-Control-Timer. A
separate control timer is used for each slave. This timer expires if response data is not correctly
transmitted by the slave within the monitoring interval. The user is informed when this happens. If
the automatic error reaction (Auto-CLEAR) has been enabled, the PROFIBUS Master exits its
OPERATE state, switches the outputs of all assigned slaves to the fail-safe status and changes to
the CLEAR state.
 Monitoring at the Slave
Slave devices use a watchdog to detect failures of the master or the bus. If data communication with
the master does not occur within the set watchdog time interval, a 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.
1-1-7

Network Operation Modes

PROFIBUS DP distinguishes four different network operation modes:
 OFFLINE
Communication with all PROFIBUS DP participants (masters and slaves) is stopped. The Master
ceases to access the PROFIBUS network.
 STOP
Cyclic communication as well as PROFIBUS DP-V1 Class 1 communication between the master
and its slaves is stopped. Only PROFIBUS DPV1 Class 2 communication and communication
between the master and other masters are still 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 writ-
ing zeros to the outputs of the slaves.
 OPERATE
The master exchanges data with its assigned slaves. Inputs are read and outputs are written. Also,
the master cyclically sends its local status to all its assigned PROFIBUS DP slaves (using a broad-
cast message).
The PROFIBUS Master Unit will always be in one of these four modes. Mode transitions from one
mode to another will be performed via intermediate modes. For example, a mode transition from
OFFLINE to OPERATE, will be performed as OFFLINE
CJ-series PROFIBUS Master Unit Operation Manual for NJ-series CPU Unit (W509)
1 Features and System Configuration
  
STOP CLEAR OPERATE.
1
1-7