Which products are affected?
ESP-DDS1-x (Drive PLC Developer Studio Version 1.4)
What happens?
After downloading the DDS project into the target system (PLC) and starting the program, the PLC_PRG unit is not processed. Moreover, a PEr Trip can be activated by the target system.
When does the problem occur?
The problem occurs depending on the number of units used in the DDS program (Program Organisation Units = POU), i.e. the number of indices assigned by DDS for the units exceeds 300.
The individual units are called by using indices. These indices are assigned automatically by DDS whereby two units can never have the same index. The maximum number of indices available is 350. The indices are assigned as follows:
1. Indices ranging from 350 to 311 are reserved for specific system functions.
2. The indices for all remaining units (exception: PLC_PRG unit) are assigned by starting with 1.
3. The index for the PLC_PRG unit is assigned with an Offset of 10 to the last assigned index.
DDS checks for all units (except for the PLC_PRG unit) whether the index to be assigned is still 'free'. If the index is not free an error message will be generated.
If the index of the PLC_PRG unit is between 311 and 350 the response described above will occur. This error occurs if at least 301 are used. Regarding this, please consider the following:
- two indices are reserved for every function block module
- one index is reserved for every function module or program unit
- every structure also reserves one index.
Possible diagnostics?
Add the following counter function to the PLC_PRG unit (example in IL):
Declaration of the global variable:
g_nTest:INT;
Logic in the PLC_PRG unit (exemplified by IL):
LD g_nTest
ADD 1
ST g_nTest
If after starting the program the value of the global variable 'nTest' is not increased, the function description described above will occur.
Since only the cyclic task is affected by the function restriction this variable can be monitored by a module of an application task and in case of an error a response is possible.
Short-term measures/recommendations?
When using the Drive PLC Developer Studio Version 1.4 check whether the PLC_PRG is processed, e.g. by applying the measures described under the topic 'possible diagnostics'.
The function restriction has been eliminated with the Drive PLC Developer Studio software, version 2.x. If this function restriction occurs we recommend carrying out an update to version 2.x.
Evaluation:
By applying the measure described under the topic 'possible diagnostics' the function restriction can be identified directly after the download or start of the project. If the measures are not used the function restriction can be detected during commissioning at the latest.
An existing DDS project in which this function restriction does not occur will still work properly as long as no further libraries, modules or structures are inserted into the DDS project.
