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+--- Thread: Modbus cyclic writes (/showthread.php?tid=6056)
Modbus cyclic writes - Smeagol - 21.07.2025
Hi,
I have a modbus slave on which i want to write a register periodically. Can this be done via the Modbus UI? I have the following profile prepared:
Code:
{
"manufacturer": "IDM",
"description": "Heat Pump Injection",
"mapping": [
{
"name": "Current Injection",
"bus_datatype": "float32",
"type": "register",
"address": 74,
"writable": 1,
"write_only": 1,
"datatype": "float32",
"units": "Kw",
"read_swap": true,
"value_multiplier": "0.001"
}
]
}But i have no clue when the value will be written? Is it only on mapped address change? Of can it be set to update no matter what every 30 seconds? If so, how? Or should this be done differently?
Thanks for the help!
RE: Modbus cyclic writes - Daniel - 21.07.2025
It is on write to the mapped object, create a resident or scheduled script which will write periodically to this object.
RE: Modbus cyclic writes - admin - 21.07.2025
This should be helpful: https://forum.logicmachine.net/showthread.php?tid=1878
RE: Modbus cyclic writes - Smeagol - 21.07.2025
Thanks!
RE: Modbus cyclic writes - Smeagol - 21.07.2025
Follow up question. For reads i need to use the swap_read option. I thus assume i should also swap the write (words) as i attempt to write a float32, meaning two 16 bit registers. Since i send a group address, how can i swap the words? I do not see an option for this in the profile (documentation profile json).
RE: Modbus cyclic writes - admin - 21.07.2025
read_swap works for both reading and writing.