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1-4
Section
Device types
7
1-4-4 Protection mechanisms
PROFIBUS-DP
provides
effective
protection
functions
against
parameterisation errors or failure of the transmission equipment. Time
monitoring is provided at the DP master and at the DP slaves. The monitoring
interval is specified during the configuration.
•
Protection mechanism at the master.
The DPM1 master monitors data transmission of its active slaves with the
Data_Control_Timer. A separate control timer is used for each slave. This
timer expires, when correct data transmission does not occur within the
monitoring interval.
If the master’s Auto_Clear Mode has been enabled, the DPM1 will exit its
Operate state, switches the outputs of all assigned slaves to fail-safe status
and changes to its Clear status (see also section 1-4-5).
•
Protection mechanisms at the slave.
The slave uses the watchdog control to detect failures of the master or the
transmission line. If no data communication with the master occurs within the
watchdog control interval, the slave automatically switches its outputs to the
fail-safe status. This mechanism can be enabled or disabled for each
individual slave.
Also, access protection is available for the inputs and outputs of the DP
slaves operating in multi-master systems. This ensures that direct access
can only be performed by the authorised master. For all other masters, the
slaves offer an image of their inputs and outputs, which can be read from any
master, even without access rights.
1-4-5 Network states
PROFIBUS-DP distinguishes four different network states.
•
Off-line
Communication between all PROFIBUS-DP devices on a network is
stopped.
•
Stop
Communication between DPM1 and DP slaves is stopped. Only
communication between DPM1 and DPM2 is possible.
•
Clear
DPM1 master attempts to set parameters, check the configuration, and
subsequently perform data exchange with its associated DP-slaves. The
data exchange comprises reading the inputs of the DP-slaves and writing
zeros to the outputs of the DP-slaves.
•
Operate
DPM1 master exchanges data with its assigned slaves, inputs are read and
outputs are written. Beside this, the DPM1 cyclically sends its local status to
all assigned DP slaves (using a multicast message) at a configurable time
interval.
When an error occurs during the data exchange phase of the DPM1, the
’Auto_clear’ configuration parameter determines the subsequent actions. If this
parameter is set to false, the DPM1 remains in the Operate state. If set to true,
the DPM1 switches the outputs of all assigned DP slaves to the fail-safe state
and the network state changes to the Clear state.
Time monitoring
At the master
At the slave
Off-line
Stop
Clear
Operate
Auto_clear