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| 2/22/2013 5:30 PM | |
Joined: 12/1/2009 Last visit: 2/9/2025 Posts: 672 Rating:
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Hi hamletd , in your actual configuration you dont have much options. 1. Try to increase the baud rate 2. Try to reduce the number of requests (combining write bits + registers in one write command) In order to do that you need to transfer you bit information into 16bit registers. That is unfortunately not always possible. You can alsoadda secondCP341, butits a quite expensive solution. |
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| 2/22/2013 5:32 PM | |
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Posts: 3093 Rating:
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Hello Hamletd, the way you do it is just perfect. The only way to increase the speed is to use two CPs. Our friend Smiffy posted an excellent comment regarding Modbus RTU communication speed. Regards, Kaulquappe |
| 2/22/2013 5:50 PM | |
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Joined: 12/1/2009 Last visit: 2/9/2025 Posts: 672 Rating:
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Hi hamletd, As I see you only write data. But do you need to write all the data cyclically? Why do you not writeupon changeor after max. elapsed time? I believe that is the best performance you can get. No need of second CP. |
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| 2/22/2013 9:40 PM | |
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Posts: 3093 Rating:
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Hello Miguel, when you use two CPs, you have two callsof P_SND_RK and P_RCV_RK with different instances. One for each LADDR of the CP. Regards, Kaulquappe |
| 2/23/2013 6:42 AM | |
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Joined: 12/1/2009 Last visit: 2/9/2025 Posts: 672 Rating:
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Dear hamletd , the bottle neck in the Modbus communication is not between your slaves and the CP. It is between the CP and the CPU.If you take a closer look into the manual you will find an interesting statementthat says, that the communication blocks can take several cycles in order to transfer the data between the CPU and the CP. That means you can try to put the communication into an interrupt OB with a short execution time. If thatsstill too slow for you, you need to distribute the load by connecting 10 slaves to each CP. Welcome to Modbus with SIMATIC |
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| 2/25/2013 4:39 PM | |
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Posts: 3093 Rating:
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Hello Hamletd, a profibus / Modbus gateway may decrease the transfer time. But this would only be possible when the gateway polls the slaves independently. You should keep in mind, that you can't decrease the time which the characters need to be transferred on the line. I searched the web and found - unfortunately in German: http://www.wachendorff.de/wp/fileserver/manual/HD67561.pdf Regards, Kaulquappe |
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