5 Commissioning and Operation
Kübler Group
16 - EN
HB Modbus Interface - R67048.0002 - 02
5.3.3 LRC check
In ASCII mode, the messages are subjected to an error check based on a longitudinal redund-
ancy check.
The check calculation (LRC) follows the content of the message without the initial 'colon' and
the two final CRLF characters. The LRC check takes place regardless of the parity check
method used.
The LRC field has a one-byte length and contains a 8-bit binary value. The LRC value is calcu-
lated by the transmitter and attached to the message. On receipt of the message, the receiver
calculates a LRC and compares this calculated value with the value contained in the LRC field.
If both values are not equal, an error is triggered.
The LRC is formed by adding successive 8-bit blocks of the message. Possible carries are ig-
nored. Then the two's complement of the result is formed. The calculation is performed with the
bytes of the message, before the coding of every byte in the two ASCII characters that corres-
pond to the hexadecimal representation of every nibble. It considers neither the 'colon' at the
beginning of the message nor the two CRLF characters at its end.
5.3.4 Data Addresses
Modbus bases its data model on a series of tables with characteristic features. The four primary
tables are:
Main tables
Object type
Type
Description
Discrete input
Single bit
Read-only
This data type can be provided by
an I/O system
Coils
Single bit
Read-write
This data type can be modified by
an application
Input register
16-bit word
Read-only
This data type can be provided by
an I/O system
Read holding
register
16-bit word
Read-write
This data type can be modified by
an application
The distinctions between inputs and outputs and between bit-addressable and word-address-
able data elements have no influence on the behavior of the application.
All data addresses in Modbus messages are zero-based.
• Holding register 40001 is addressed as Register 0001 in the data address field of the mes-
sage. The function code field already defines a 'holding register' operation.
Therefore reference '4XXXX' is implied.
• Holding register 40014 is addressed as register 0x0D (14 decimal).
5.4 Function code 03 - Reading the Holding Register
Read Holding Registers function code 03 (0x03)
Reads the binary content of the holding registers (4XXXX references) in the slave.
NOTICE
Broadcast function
Broadcast is not supported
