LAUMAS WLIGHT - Modbus-RTU Register Operations; Reading Holding Registers; Writing Multiple Registers

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Interrogation frequency is linked to the communication speed set (the instrument stands by for at
least 3 bytes before starting calculations an eventual response to the interrogation query). The
 parameter present in the SERIAL COMMUNICATION SETTING section, allows the
instrument to respond with a further delay and this directly influences the number of interrogations
possible in the unit of time.
For additional information on this protocol refer to the general technical specifications
PI_MBUS_300.
In general queries and answers toward and from one slave instrument are composed as follows:
FUNCTION 3: Read holding registers (READ PROGRAMMABLE REGISTERS)
QUERY
Address
Function
1st register address
No. registers
2 byte
A
0x03
0x0000
0x0002
CRC
Tot. byte = 8
RESPONSE
Address
Function
No. bytes
1st register
2nd register
2 byte
A
0x03
0x04
0x0064
0x00C8
CRC
Tot. byte = 3+2*No. registers+2
where: No. registers .. number of Modbus registers to write beginning from the address no. 1
No. byte ........ number of bytes of the following data
FUNCTION 16: Preset multiple registers (WRITE MULTIPLE REGISTERS)
QUERY
Address
Function
1st reg. add.
No. reg.
No. bytes
Val.reg.1
Val.reg.2
2 byte
A
0x10
0x0000
0x0002
0x04
0x0000
0x0000
CRC
Tot. byte = 7+2*No. registers+2
RESPONSE
Address
Function
1st reg. address
No. reg.
2 byte
A
0x10
0x0000
0x0002
CRC
Tot. byte = 8
where: No. registers .. number of Modbus registers to read beginning from the address no. 1
No. byte ........ number of bytes of the following data
Val.reg.1 ....... contents of the register beginning from the first
The response contains the number of registers modified beginning from the address no. 1.