EtherCAT Function Blocks that Work with Drive Parameters
These function blocks are used to work with drive parameters not supported by ML and MC function blocks.
- They support reading and writing drive parameters using the non-cyclic SDO channel in the EtherCAT network.
- The ASCII name for the parameter is used as an input.
Execution Time
These function blocks typically take a longer time to execute (up to ten cycles to finish executing).
It takes the same amount of time to Read or Write a parameter.
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It takes more than one cycle to execute these function blocks (but less than 100 ms).
See When can I expect my SDO command to be completed? in the FAQs on how to set up the update rate for SDO communication.
Reason
It is not only linked to the ASCII SDO communication. Because these FBs are waiting for the AKD drive to responds, the execution time can also increase due to the load of the AKD firmware at the time you call them.
Result
The PLC code is overrunning the cycle duration. as explained in Tasking Model / Scheduling.
As a consequence, you can see this message in the Controller Log window:
Solution
When this happens we recommend:
- Use these function blocks sparingly in programs
- Rely on the EtherCAT read/write SDO function blocks
- Smooth the load of the PLC code by executing these function blocks at the required update rate.
Stats about the FB Execution Time
- There is a small difference in timing when running EtherCAT at 2ms compared to other frequencies.
0.25, 0.5, 1ms 2ms Mean 9ms 14ms Min 3ms 8ms Max 16ms 24ms - Max time to consider when executing a single SDO command, (i.e., before the Done output becomes TRUE): 24ms.
- Max time to consider when executing a single Drive Parameter command (i.e. before the Done output becomes TRUE): 60 ms.
4 kHz 1 kHz Mean 20 ms 11 ms Min 15 ms 9 ms Max 45 ms 58 ms - When sending multiple commands to a single drive, only one command can be sent at a time.
- The time to execute multiple commands is:
Number of commands x Execution time of a single command
- The time to execute multiple commands is:
- When commands are sent to different AKD drives at the same time, the requests do not interfere with each other.
- The function finishes execution in the same maximum time as one drive.
