Process Station ABB FieldController 800
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4 Processing and failure action
4.1 Automatic error handling at task level
Error handling at task level is described in the flow chart (page 39).
When an error is identified in a user program, an error task is executed once. The error- task is
the highest priority task (priority 100) of a resource and is used to handle errors in user programs
by user programs. In the case of non-recoverable errors, the error-generating task changes to the
unrunnable state; in the case of recoverable errors it is possible to continue running the error-
generating task, provided the automatic error correction for the D-PS resource is switched on.
Owing to its high priority it cannot be interrupted by other tasks. Execution of the error task can be
suppressed.
Error handling at task level is switched on by default but can be deactivated in the resource con-
figuration (see Engineering Manual, System Configuration, Project tree). When deactivated,
an error causes the task to change to the unrunnable state, even if the error is recoverable. The
error appears in text form in the task header and the object number of the faulty project object is
also displayed.
If automatic error handling is active and a recoverable error is detected, the affected task remains
in the running state. In this case, the error condition is ascertainable only by evaluation of the
system variables.
Each runtime error detected during execution of a command results in an entry recording the
cause and location of the error in system variables specially predefined for error handling. The
cause of the error, e.g. 4 for UINT div. by 0, is saved in the variable “ErrorNo”. The variable “Er-
rorProgra” is written with the object number of the program or function block that caused the error.
Furthermore, the object number of the affected task is saved in the variable “ErrorTask,” but only
displayed in the task header if error handling is deactivated. The affected object can then be lo-
calized in the object list with its name, state, type and position in the project tree. If the affected
task, the one which triggered the error, is not the error-handling task, the error-handling task itself
is now triggered. Error handling specific to the cause of the error and/or its location can be un-
dertaken in this task, with the aid of the system variables.
If an error should occur in the error-handling task itself, the error-handing task is signaled as un-
runnable.
See also Engineering Manual, IEC 61131-3 Programming, Variables, System Variables.
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