Beckhoff FC3101, Documentation

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FC310x as master
FC3101 and FC3102 19 Version: 3.0
Monitoring in the slave
In order to monitor failure of the master and data transmission on the PROFIBUS, a watchdog (see the
box's PROFIBUS [
}
58] tab) can be activated (default setting: watchdog activated with 200 ms). The
Watchdog must be set to at least twice the maximum Estimated Cycle Time and Cycle Time (see
"FC310x" tab (for TwinCAT 2.8 [
}
40] or TwinCAT 2.9 [
}
48] ) of the master).
Failure of the PLC/IO task
A distinction is made between a PLC stop, reaching a break point and a task stop (the I/O task and NC task
are only stopped when the entire system stops). In the case of a PLC stop, the output data is set to 0 by the
PLC, whereas when a breakpoint is reached the data initially remains unchanged.
In the master, the task is monitored with a monitoring time (TwinCAT 2.8: according to the setting Clear
Delay x task cycle time on the PROFIBUS [
}
42] tab of the master, TwinCAT 2.9: according to the setting
Task Watchdog x task cycle time in the Fault Settings [
}
51] dialog). If no new data transfer takes place
within this monitoring time, the master switches to "Clear" state according to the setting Reaction on PLC
Stop or Reaction on Task Stop (TwinCAT 2.8: see PROFIBUS [
}
42] tab of the master, TwinCAT 2.9: see
Fault Settings [
}
51] dialog) (outputs are set to 0 or safe state (Fail_Safe = 1 in the GSD file, default setting)
or remains in "Operate" state (outputs retain the last value). The "Operate" setting is valuable when the
outputs should not be cleared when a breakpoint is reached in the PLC. However, if the PLC stops, the
outputs will still be set to 0 (by the PLC), even if the master remains in the "Operate" state. It should,
however, be noted that the outputs will only be zeroed if the previous DP cycle is completed in time (see the
Synchronization [
}
12] chapter). It should therefore only be set during the commissioning phase.
Failure of the host
To monitor a host crash (e.g. blue screen on a PC), a watchdog time can be set (TwinCAT 2.8: see FC310x
[
}
40] tab of the master, TwinCAT 2.9: see Fault Settings [
}
51] dialog). If this watchdog timer elapses, the
master enters the OFFLINE state, so that the DP connections to all the slaves are removed, and the master
logs off from the PROFIBUS, ceasing to carry out bus accesses.
Start-up behavior
The DP connections to all the slaves are established when the TwinCAT system starts up. Until the highest
priority task that is involved has not been started, the master still does not send any Data_Exchange
telegrams even after the DP connection has been established, and sends only diagnostic telegrams. As
soon as the highest priority task has transferred data once, and the DP connection for the corresponding DP
slave has been established, the master cyclically (with the highest priority assigned task) sends one
Data_Exchange telegram to each of the corresponding slaves.
In addition, the Operate Delay and Clear Mode settings (TwinCAT 2.8: see PROFIBUS [
}
42] tab of the
master, TwinCAT 2.9: see Fault Settings [
}
51] dialog) can be used to specify when the master switches
from "Clear" state (outputs are set to 0 or safe state (Fail_Safe = 1 in the GSD file)) to "Operate" state
(outputs correspond to the outputs transferred by the task). The
Operate Delay specifies the minimum
length of time for which the master should remain in the "Clear" state following the first transfer of data. As
has been described above, the
Clear mode specifies whether the master changes into or remains in the
"Clear" state if a slave in general or an MC slave in particular fails.
Shut-down behavior
The reaction to the stopping of the TwinCAT system is exactly the same as has been described above in the
"Failure of the Host" chapter; the DP connections to all slaves are removed, and the master logs itself off
from the bus.