Protection Mechanisms; Network States - Omron CJ1W-PRT21 Operation Manual

PROFIBUS-DP characteristics
1-4-4

Protection mechanisms

Time monitoring
At the master
At the slave
1-4-5

Network states

Off-line
Stop
Clear
Operate
Auto_Clear
PROFIBUS-DP provides effective protection functions against parameterisa-
tion errors or failure of the transmission equipment. Time monitoring is pro-
vided at the DP master and at the DP slaves. The monitoring interval is spec-
ified 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 moni-
toring interval.
If the master's Auto_Clear mode is enabled, the DPM1 exits the 'Operate'
state, switches the outputs of all assigned slaves to fail-safe status, and
changes to its 'Clear' state (see also 1-4-5 Network states ).
• 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 individ-
ual 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 other masters, the slaves
offer an image of their inputs and outputs, which can be read by any master,
even without access rights.
PROFIBUS-DP distinguishes four different network states.
• Off-line
Communication between all DP participants is stopped.
• Stop
Communication between DPM1 and DP slaves is stopped. Only communica-
tion between DPM1 and DPM2 is possible.
• Clear
DPM1 master attempts to set parameters, check the configuration, and sub-
sequently perform data exchange with its associated DP-slaves. The data
exchange comprises reading the inputs of the DP-slaves and writing zero's 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 (with a multicast message) at a configurable time
interval.
When an error occurs during the data transfer phase of the DPM1, the
'Auto_Clear' configuration setting 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.
Section 1-4
7