I/O System S900
Communication Interface for PROFIBUS DP, CI920
Polling the passive CI920 is used for monitoring the second, passive bus line.
Correct transmission of both CI920’s can only be monitored by the DP master.
If the DP master does not receive a response from the active CI920 for a
request, the slave handler must be reset. This way the slave can detect that
the DP master no longer recognizes the slave in the state “Data Exchange”
and can react with a switching operation. Otherwise the DP master would
continue to transmit Data Exchange telegrams and the slave cannot detect
that its own transmission function is malfunctioning.
Switching criteria
The DP watchdog of the active CI920 responds and
•
the passive CI920 is ready to take over,
•
the passive CI920 is at least in state “Baud_Control” (FDL status
polling),
•
the passive CI920 is present,
•
the active CI920 has failed and see above.
Diagnostics / behaviour in case of failure
The only trouble-shooting procedures that may be necessary are related to
configuration and parameter errors, provided that the S900 modules are used
properly according to the specifications. S900 has special indicator LEDs
allowing you to figure out errors and their possible reasons quickly. A
PROFIBUS diagnostic message is provided for all errors indicated locally
through the LEDs.
When a module is replaced (with an equivalent module), the new module is
automatically configured/parameterized according to the following table:
Table 4-4 Data source in case of module replacement
Data Source
CI920 Fieldbus
master
Redundant CI920
Active CI920
I/O module
CI920
Behavior of outputs in error case
I/O module
Behavior of inputs in error case
Active CI920
S900 is a user-friendly and easily serviceable system. As you can see from the
descriptions above, it allows for a 'plug-and-play' kind of replacement. No
engineering tool is required.
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