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6-2 The fieldbus interface Interbus
6.3
SYNAX
Monitoring the fieldbus transmission - behavior with bus
failures
As described in section 4.5 the DBS is equipped with a bus monitor that
uses a watchdog timer to quickly respond to a bus failure.
Note:
The following fieldbus objects for determining action in case
of a bus failure can only be write accessed as standard
objects by the bus master.
Watchdog function
The PLC and the fieldbus master specify time via object
6003
PD watchdog time
in [ms] after which the error reaction is started after a fieldbus failure. The
watchdog is switched off if object 6003 is set to "0xFFFF“. The default
value is 300ms.
Note:
When setting PD watchdog time it should be taken into
account that fieldbus cycles can fail under normal operating
conditions.
Error reaction with bus failure
The DBS permits a setting of two error reactions for the process data
channel that can meet various demands. Using object
6004
error reaction PD channel
there are two options, namely, the data are either frozen or deleted. The
basic setting is to freeze the data and to be able to perform an error
reaction by the CLC.
Note:
Output data freezed
(default setting)
For a non-resident storage of new values for fieldbus objects,
use object 5E7D. Note, however, that the hardware of the
fieldbus module cannot be simply exchanged if servicing
should become necessary.
The output data are freezed at the end of the watchdog time if a value
not equal to 0xFFFF has been entered in object 6004 (default value = 0).
This means that the last data to arrive at the DBS remain effective.
The CLC-D is informed of a bus failure by an active watchdog in the
fieldbus status register. If the CLC is in operating mode, then output
"fieldbus - real time channel active“ (_A:C01.08) is cleared. This CLC
output can be used to bring the axes to standstill with the I/O logic in
case of a bus failure.
With a bus return, output "fieldbus - real time channel active“ (_A:C01.08)
is set. The PLC briefly resets the output data to then assume the
specified values.
Output data cleared
If 0xFFFF is entered into object 6004, then the output data are internally
cleared on the DBS if the fieldbus fails and watchdog time has run out. In
other words, if the drive enable of an axis is applied directly via an
external input, then the drive enable is cleared.
DOK-SYNAX*-SY*-06VRS**-FK01-EN-P