Endress+Hauser Liquiline CM44 series - Modbus Exception Codes; Transmission Modes; Ascii

SD01189C/07/EN/04.17
Endress+Hauser
7
3.2.2 Modbus exception codes
If the MODBUS slave detects an error in the request telegram from the master, it replies to the master with
an error message comprising the slave address, function code, error code (exception code) and checksum.
To indicate that it is an error message, the leading bit of the returned function code is set. The cause of the
error is transmitted to the master via the error code (exception code).
Exception Code
Info
01
ILLEGAL_FUNCTION
The function code sent by the master is not supported by the measuring device (slave).
02
ILLEGAL_DATA_ADDRESS
The register addressed by the master is not assigned (i.e. it does not exist), or the length
of the data queried is too long.
03
ILLEGAL_DATA_VALUE
The master attempts to write to a register which allows only read access.
The value that appears in the data field is not permitted: e.g. range limits have been
exceeded or the data format is incorrect.
04
SLAVE_DEVICE_FAILURE
The slave has not replied to the request telegram from the master, or an error has
occurred while processing the request telegram.
3.3 Transmission Modes
There are three data transmission modes: ASCII, RTU and TCP.
3.3.1 ASCII
The data are transmitted as ASCII characters and are therefore readable by humans.
Start
Address
Function
Data
LRC
End
1 character
2 characters
2 characters
N characters
2 characters
2 characters
= „:“
CRLF
Field
Length
Info
Client
Server
Address
2 Byte
Identifies the target device
Set by the client
Copied from the
request into the
reply
LRC
2 Byte
 Modbus specification
Set by the client
Set by the server