Payload Structure

Data Types

Code	Data Type	Description
00	INT16	16-bit signed integer
01	UINT16	16-bit unsigned integer
02	INT32 [MSB]	Most significant 32-bit signed integer
03	INT32 [LSB]	Least significant 32-bit signed integer
04	FLOAT32 [MSB]	Most significant 32-bit floating-point number
05	FLOAT32 [LSB]	Least significant 32-bit floating-point number

Payload Structure

Parameter	Type	Description	Default	Valid Range
Field	Integer	Data field identifier	1	1–255
slaveld	Integer	ID of the slave device	1	1–247
functionCode	Integer	Function code for the operation (e.g., read, write)	3	1–6, 15, 16
Enable	Integer	Enable flag (1 for enabled, 0 for disabled)	1	0 or 1
datatype	Integer	Specifies the data type of the value to read	01	00–05
groupParaNo	Integer	Number of registers in a single group	1	1–125
Registeraddress	Integer	Address of the registers	0	0–65535

One-Time Modbus Register Read

Example payload (JSON):

{ 
"slaveId": 1, 
"functionCode": 3, 
"dataType": 1, 
"numberOfParameters": 1, 
"Registeraddress": 257
}

note

Use FPort = 13

One-Time Modbus Register Write

Parameter	Type	Description
slaveId	Integer	ID of the slave device
numberOfRegisters	Integer	Number of registers to write (e.g., 1 for INT16)
address	Integer	Address of the register to write
value	Integer	Value to write into the register

How to write registers from server ?

• Example

{ 
    "slaveId": 1,
    "numberofreg": 1,
    "address": 0,
    "value": 223
}

How to write coils from server ?

• Example

{ 
    "slaveId": 10,
    "numberofreg": 1,
    "address": 0,
    "value": 65280
}