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+--- Thread: Modbus limits (/showthread.php?tid=6325)
Modbus limits - gdimaria - 24.02.2026
Hi,
A customer of mine asked me for a quote to connect 30 modbus multimeters via TCP to the LM.
For each multimeter, 25 registers need to be mapped.
The multimeters are grouped in two different IP address.
Is this possible?
Are there memory limits on the LM?
RE: Modbus limits - Daniel - 24.02.2026
What do you mean by two different IP addresses? Do you use Modbus IP gateway?
RE: Modbus limits - gdimaria - 24.02.2026
(24.02.2026, 14:46)Daniel Wrote: What do you mean by two different IP addresses? Do you use Modbus IP gateway?
I mean that there will be 18 multimeters with the same IP address and different IDs.
and another 12 on a different IP with different IDs.
RE: Modbus limits - Daniel - 24.02.2026
Its OK
RE: Modbus limits - gdimaria - 25.02.2026
(24.02.2026, 20:53)Daniel Wrote: Its OK
Good!
By the way, is there a limit on the number of registers I can map to a single device in LM? And how many Modbus devices can I connect simultaneously?
Thank you
G.
RE: Modbus limits - Daniel - 25.02.2026
By the software there is no limit but the more you add the longer it will take to read all of them and you must adjust pooling interval accordingly. It is single queue for all.
RE: Modbus limits - gdimaria - 25.02.2026
(25.02.2026, 08:15)Daniel Wrote: By the software there is no limit but the more you add the longer it will take to read all of them and you must adjust pooling interval accordingly. It is single queue for all.
a single queue for all devices? So how it works when I set different polling time for each or a part of the devices? Anyway, what polling time could be good for 30 devices like that?
RE: Modbus limits - Daniel - 25.02.2026
Nr of registers x timeout is the safest way.
RE: Modbus limits - admin - 25.02.2026
Using a profile with block read can significantly speed things up. Make sure to use persistent connection mode for all devices.
RE: Modbus limits - gdimaria - 25.02.2026
(25.02.2026, 15:42)admin Wrote: Using a profile with block read can significantly speed things up. Make sure to use persistent connection mode for all devices.
how to set profile with block read? Your Modbus Profiler app allows it?
RE: Modbus limits - Daniel - 25.02.2026
Yes you can, in Advance you must add read_count and read_offest. Good example is this
https://forum.logicmachine.net/showthread.php?tid=4687&highlight=read_count
Basically you set register for all the same and read count define how many registers you will read at once (up 125) and it should be the same for all registers in same block. Read_offset is the offset navigating to real register number counting from the register address.