Error Messages; Modbus Error Codes - ECOLAB Versatronic Modbus Beschreibung

3.8

Error messages

3.8.1

Modbus error codes

Requirements for Modbus communication
The following conditions must be met for a slave to receive, process, and respond to
queries:
n Baud rate and data format of master and slave must match.
n The correct slave address must be used in the query.
Slave devices respond only after a successful checksum check of the query by the
n
slave. Otherwise, the query is rejected by the slave.
n The instruction from the master must be complete and conform to the Modbus
protocol.
n The number of words to be read must be greater than 0.
Error codes
If the data query from the master has been received by the slave without transmission
errors but cannot be processed, the slave responds with an error code. The following error
codes may occur:
n 01 = invalid function; the function codes supported by the Versatronic are listed in
Ä Chapter 3.4 'Function codes' on page 17
n 02 = Invalid address or too many words or bits should be read or written
n 03 = Value is outside the admissible range
n 08 = Value is write-protected
Response to malfunction
Slave address
1 byte
The function code is OR-gated with 0x80. As a result, the highest-value bit (msb) is
set to 1.
Example
Data query:
01
Slave
Response (with error code 2):
01
Slave
Response with error code 02, because the address 0x2345 does not exist.
Function XX OR 80h
1 byte
06 23 45
Write word Word address
86
OR function
25
Modbus protocol description
Error code
1 byte
00 01
Word value
02
Errors
417102397 Rev. 1-10.2019
Checksum CRC
2 bytes
52 5B
CRC
C3 A1
CRC