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+--- Thread: ModBus TCP slave problem (/showthread.php?tid=2877)
ModBus TCP slave problem - AlexLV - 29.09.2020
Hi,
need a little explanation from more experienced persons.
I use LM like Modbus TCP slave device. I need read/write over it to KNX devices. All was done fine and works, till I need to add one more, 12th knx thermostat.
I used 124 registers. When I added new device and add registers, I found out I cannot read over 125 register or write over 123.. Is possible to solve somehow this problem? At scanner max 125 registers (picture below), and I cannot read as example register 126..
BR,
Alex
RE: ModBus TCP slave problem - admin - 30.09.2020
These limits are defined by the modbus standard. You can send two or more read/write commands in your case.
RE: ModBus TCP slave problem - AlexLV - 30.09.2020
Yes, I read about it, but how I need request or read as example Holding register 133 or group from 140 to 200 registers from LM? I tried this tool in above my post but not found how to do it..
How many registers I can use in LM as a TCP Modbus Slave in total?
Also may be in future will be possible to make work with modbus Slave script as example Modbus address, KNX group, datatype for easiest edit if needed? Now just table way one by one groups and then datat ypes, a little problematic if to many registers is used..
Alex
RE: ModBus TCP slave problem - admin - 30.09.2020
You can read up to 125 registers at once via TCP, it does not matter what is the starting address. Use this tool for testing: https://github.com/ed-chemnitz/qmodbus/releases/tag/v0.3.0
In theory you can use all 65536 registers/coils/etc.
We have plans to create a modbus slave app where you can easily map group addresses to modbus registers/coils.
RE: ModBus TCP slave problem - AlexLV - 30.09.2020
Thank you for so correct answers