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+--- Thread: Modbus data types breaking change in latest FW? (/showthread.php?tid=6585)
Modbus data types breaking change in latest FW? - myg - 31.10.2026
After I installed latest firmware (had previous one before), I have a strong suspicion that something happened with modbus profile calculations since reading resolution dropped significantly. Here's screenshot of the readings where you can see a sharp drop in precision:
Below is my profile.
From the sniffer data (one example), i receive 0x2D5 which should decode to 725*0.0625 = 45.31C, but data written to bus is 46C.
I had suspicion that this happens due to wrong datatype applied during conversion. Since field called "modbus register datatype", i used int16 with 0.0625 multiplier. This worked previously. I've tried to change datatype to float16, but result was unexpected - all calculated values became /100, so i had to update multiplier to 6.25 to compensate for that.
I'm not seeing this behavior mentioned in documentation , nor in the changelog of the firmware.
Is this a bug, or should i update all profiles? is this a correct way to "fix" calculations?
Code:
{
"manufacturer": "WirenBoard",
"description": "WB-M1W2 Temperature",
"mapping": [
{
"bus_address": "32/4/1",
"value_delta": 0.1,
"datatype": "int16",
"bus_datatype": "temperature",
"type": "inputregister",
"address": 3584,
"value_multiplier": 0.0625,
"bus_write": false,
"name": "Temperature 1:1"
},
{
"bus_address": "32/4/2",
"value_delta": 0.1,
"datatype": "int16",
"bus_datatype": "temperature",
"type": "inputregister",
"address": 3585,
"value_multiplier": 0.0625,
"bus_write": false,
"name": "Temperature 1:2"
},
{
"bus_address": "32/4/3",
"value_delta": 0.1,
"datatype": "int16",
"bus_datatype": "temperature",
"type": "inputregister",
"address": 3624,
"value_multiplier": 0.0625,
"bus_write": false,
"name": "Temperature 2:1"
},
{
"bus_address": "32/4/4",
"value_delta": 0.1,
"datatype": "int16",
"bus_datatype": "temperature",
"type": "inputregister",
"address": 3625,
"value_multiplier": 0.0625,
"bus_write": false,
"name": "Temperature 2:2"
}
]
}after further testing i think i found more interesting details:
all problems are happening with bus_datatype=temperature, which is a subset of float16 (so i assumed it will have identical behavior). Also it causes rounding errors which returns slightly incorrect values.
if i use bus_datatype=float16 with datatype=int16 and 0.0625 multiplier then everything seems correct.