Which products are affected?
ESP-DDS2-P (Global Drive PLC Developer Studio Version 1.x, 2.0, 2.1)
What happens?
In the
Task configuration (
Resources tab) an event-controlled task is defined which has to be started depending on a system variable. If the system variable becomes TRUE, however, that task is not executed.
Example:
An event-controlled task is to be started by the digital input E1. Although the digital input is TRUE (switched on), the program block attached to the task is not executed.
When does the problem occur?
The system block and hence the system variable which is to start the event-controlled task are only used in this event-controlled task. Depending on the DDS version, process image creation varies for that system block:
- DDS V1.x: No process image is created for the system block.
- As of DDS V2.0: The process image is created by the event-controlled task. An update of the process image only takes place if the task is called up. However, the event-controlled task is only called up if in the process image of the system variable a positive edge is detected.
That is, in both cases the process image of the system variable is not updated so the event-controlled task is not started.
Possible diagnostics?
In the dialog
Process mirror (tab
Resources>Process Mirror) check whether a process image is created for the system block of this system variable and whether it is created in the task which is to be started by that system variable.
Short-term measures/recommendations?
Program an instruction with the system variable in a block which is called by a time-controlled user task or the cyclic task. This task is then responsible for creating the process image of that system variable.
Evaluation:
This function restriction is recognised upon commissioning at the latest because owing to the function restriction an event-controlled task is not started by the system variable. Definition of event-controlled tasks tends to be rare.
