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+--- Thread: Modbus RTU (/showthread.php?tid=4583)
Modbus RTU - hoangknx - 15.02.2023
Hello everyone. I am having trouble using Modbus RTU1 to link the LM5-KC to the DTA of a DAIKIN air conditioner. Once connected, Using visualization is very delay
Do you experience this issue? And what about fixing? I sincerely appreciate it.
RE: Modbus RTU - Daniel - 15.02.2023
This is a lot of requests, how often do you pool?
RE: Modbus RTU - hoangknx - 15.02.2023
(15.02.2023, 08:41)Daniel Wrote: This is a lot of requests, how often do you pool?
I think so too! So how do you know there are a lot of requests? can you guide me to test it? Thank you very much
RE: Modbus RTU - Daniel - 15.02.2023
What is the pool interval?
RE: Modbus RTU - hoangknx - 15.02.2023
(15.02.2023, 13:05)Daniel Wrote: What is the pool interval?
Does it match your query?
RE: Modbus RTU - Daniel - 15.02.2023
This is too fast, make it much longer and see how it behaves. Write will be nearly instant but reading will have to be as often as pool interval.
Other alternative is to use block read but you would have to rebuild your profile and not every slave is supporting it.
RE: Modbus RTU - hoangknx - 15.02.2023
(15.02.2023, 13:28)Daniel Wrote: This is too fast, make it much longer and see how it behaves. Write will be nearly instant but reading will have to be as often as pool interval.
Other alternative is to use block read but you would have to rebuild your profile and not every slave is supporting it.
You say read the block! Could you give me an example? I am extremely grateful to you.
RE: Modbus RTU - Daniel - 15.02.2023
Like here
https://forum.logicmachine.net/showthread.php?tid=3259&pid=21034#pid21034
Address is always the same for whole block, read_count define how many registers you want to read at once (up to 125) and then you need to add read_offset to get data from specif register.
RE: Modbus RTU - hoangknx - 15.02.2023
(15.02.2023, 13:57)Daniel Wrote: Like here
https://forum.logicmachine.net/showthread.php?tid=3259&pid=21034#pid21034
Address is always the same for whole block, read_count define how many registers you want to read at once (up to 125) and then you need to add read_offset to get data from specif register.
Thank you for your help. I will respond to you after I return to the company tomorrow. Thank you very muchÂ
RE: Modbus RTU - hoangknx - 16.02.2023
(15.02.2023, 13:57)Daniel Wrote: Like here
https://forum.logicmachine.net/showthread.php?tid=3259&pid=21034#pid21034
Address is always the same for whole block, read_count define how many registers you want to read at once (up to 125) and then you need to add read_offset to get data from specif register.
Hi Daniel, I increase the polling interval period, but the delay LM increases.
RE: Modbus RTU - admin - 16.02.2023
Check that you have GND connected between LM and Modbus device, this should help with CRC and other communication errors. Also make sure that RS485 cable is not near AC cables which can break the communication due to noise.
You can speed up the communication by settings the baud rate to 19200 instead of 9600 (make sure to change on both LM and Modbus device side). As Daniel said the best way is to implement block read. When done correctly it will provide a very significant communication speed increase.
The poll interval should be set to the lowest acceptable value. But you won't get real-time status anyway. This is a basic limitation of Modbus due to the use of polling.