Function code 3 example
Query
Slave address
1 byte
Function
1 byte
Starting Address Hi
1 byte
Starting Address Lo
1 byte
Quantity of Registers Hi
1 byte
Quantity of Registers Lo
1 byte
CRC
2 bytes
Response
Slave address
1 byte
Function
1 byte
Byte count
1 byte
Register Value Hi
1 byte
Register Value Lo
1 byte
:
:
Register Value Hi
1 byte
Register Value Lo
1 byte
CRC
2 bytes
Example: Read absolute massflow (address 3000)
Query: 1,3,11,184,0,2,70,10
Slave address = 1 (0x01)
Function = 3 (0x03)
Starting Address Hi, Lo = 11, 184 (0x0B,0xB8)
Quantity of Registers Hi , Lo = 0, 2 (0x00,0x02)
CRC = 70,10 (0x46, 0x0A)
Starting address 0x0BB8 = 3000
Quantity of registers = 0x0002 = 2
Response: 1,3,4,64,195,82,139,98,200
Slave address = 1 (0x01)
Function = 3 (0x03)
Byte Count = 4 (0x04)
Register 1 - Register Value Hi, Lo = 64, 195 (0x40, 0xC3)
Register 2 - Register Value Hi, Lo = 82, 139 (0x52, 0x93)
CRC = 98,200 (0x62, 0xC8)
Absolute mass flow = 0x40C35293 = 6.10383 kg/sec
Modbus communication FCT010
C.2 Modbus function codes
SITRANS MASS 2100 & FC300 (FCT010/DSL)
152
Operating Instructions, 06/2020, A5E39788682-AB