7/27/2020 4:46 PM | |
Joined: 9/27/2006 Last visit: 9/25/2024 Posts: 12283 Rating: (2685) |
Hello sixthomas; Your questions are interesting, but you should take a step back and look at the fundamentals of PLC program processing before you continue in this research. In TIA Professional, DPRD_DAT and DPWR_DAT are instructions; in the S7-300/400 they were SFCs. In both cases, they must be called in the PLC program, which means their execution will be linked to the PLC scan cycle. You might try to call them in a cyclic OB to make them work faster than the PLC scan, but... DPRD_DAT and DPWR_DAT are asynchronous instructions, which means they will not be executed in a single scan cycle if there are operations not yet complete. They will take the amount of cycle time required to complete the call, even if it extends to a large number of scan cycles. See the following extract from the CP 1542-5 Profibus-DP master manual: https://support.industry.siemens.com/cs/ww/en/view/99489389/53701249547 Calling program blocks (instructions) for distributed I/O Several calls are necessary for the instructions of the distributed I/O. The time required to process the job depends on load, round-trip time and transmission speed. If these instructions are called in a loop within one cycle, the cycle time could be exceeded. I can only suggest you test your Profibus data exchanges based on this information and see how long (how many cycles) it takes to complete the operation of these instructions with your communication load. Hope this helps, Daniel Chartier |
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