Eaton XC-303 Series - Task Monitoring by Watchdog

4 PLC configuration
4.4 Task monitoring by watchdog
Modular PLCs XControl: XC-104-…, XC-204-…, XC-303-… 01/23 MN050005EN Eaton.com 79
Example 2:
Table 12 Task details for example 2
In example 2 in the first task the input IX4.0 is programmed and in the sec-
ond task the input IX4.1 and output QX4.0 is programmed.
At the beginning of the first task, input IX4.0 is updated. If this input is set,
output QX4.0 is set as well. Otherwise, it is reset.
At the beginning of the second task, input IX4.1 of the input module is
updated and output QX4.0 is set or reset.
As a result, the control sequence could result in output QX4.0 being set in
the first task and reset in the second. In other words, the output would be
toggled.
Creating a task with consistent inputs/outputs
Avoid access to the physical outputs from several tasks. In order to guaran-
tee a clear PLC sequence, create for the local inputs/outputs and the inputs/
outputs of the local expansion module a task in which all inputs are copied in
global variables and at the end of the interval all outputs of global variables
are written to the output module (I/O update task). The I/Os are consistent
(data integrity) within this task. The global variables can then be used instead
of the I/Os in other tasks.
4.4 Task monitoring by watchdog
The processing time of a task can be monitored in terms of time required
using a watchdog. The following applies for defining the monitoring time:
Task name Priority Cycle time
Prog 1 2 50 ms
Prog 2 1 20 ms
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Do not access the same input or output from different tasks.
￫
On the XC300 PLC a maximum of 50 tasks are possible.
The parameterization of a task as “free wheeling” is not sup-
ported.
Note with parametric programming of the watchdog time that
the POU called with the interrupt service routines, extends the
task run times accordingly.
Processing time < Interval time of the task < Watchdog(time)