66
Format: Byte
Start 1 bit
Data 8 bit
Parity 0 bit
Stop 1 bit
Format: Response frame
Address 1 byte
Function code 1 byte (or error code, see below)
Byte count 1 byte (or exception code, see below)
Register data 2 times the quantity of 16-bit register
Error check (CRC) 2 bytes
Total 7 bytes if correct (or 5 bytes if in error)
Only Function Code 03, 'Read holding registers' is allowed.
Parameters and register data
Register Parameters
0
3 - Identity
Note: When the device is an IR slave and there is a temporary error in the IR
Master-Slave comms, an offset of +32768 is added to the identification value of
that particular slave stored in the master's database.
1 Water level (%)
2 Set point (SP)
3 Control band (CB)
4 Alarm 1
5 Alarm 1 delay (S)
6 Alarm 2
7 Alarm 2 delay (S)
8 Steam offset (%)
9 Water flowrate (%)
The format of the register data is 16 bit integer, with the most significant byte transmitted first.
Exception codes
01 illegal function 02 illegal data address
Error frame structure (in hex) transmitted by the product
Parameter Byte 1 Byte 2 Byte 3 Byte 4 Byte 5
Device
Address
Function
Code
Exception
Code
CRC
(LSB)
CRC
(MSB)
Illegal function XX 83 01 XX XX
Illegal data address XX 83 02 XX XX
11. Appendix -
Summary of the Modbus protocol
Format: Request frame
Address 1 byte
Function code 1 byte
Start address 2 bytes
Quantity of registers 2 bytes
Cyclic redundancy check (CRC) 2 bytes
Total 8 bytes
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