Protection Mechanisms; Network Operation Modes - Omron WS02-9094G - V1.0 Operation Manual

Overview of PROFIBUS
1-1-6

Protection Mechanisms

Monitoring Time
Monitoring at the Master
Monitoring at the Slave
1-1-7

Network Operation Modes

OFFLINE
STOP
CLEAR
OPERATE
Auto-CLEAR
Fail-safe State
6
PROFIBUS DP provides effective protection functions against parameteriza-
tion errors or failure of the transmission equipment. Time monitoring is pro-
vided both at the master and the slave devices. The monitoring interval is
specified when the system is configured.
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.
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.
PROFIBUS DP distinguishes four different network operation modes:
• Communication with all PROFIBUS DP participants (masters and slaves)
is stopped. The Master ceases to access the PROFIBUS network.
• Communication between the master and its slaves is stopped. Only com-
munication between the master and other masters is still possible.
• 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.
• 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 broadcast 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
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 function has been
enabled, the master automatically changes the network to the CLEAR mode,
in which the outputs 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.
→ → →
STOP CLEAR OPERATE.
Section 1-1