Advant Controller AC 31 / Issued: 01.99 6 – 7 Communication
3
The MODBUS
®
frames transmitted by the master contain the following information:
- The MODBUS
®
address of the interrogated slave (1 byte)
- The function code defining the master request (1 byte)
- The data to be exchanged (N bytes)
- The CRC16 control code (2 bytes)
The frame has a maximum total length of 240 bytes, thereby enabling the exchange of a
maximum of 100 data words or 255 binary data.
The slave’s reply contains the request confirmation, the data to be returned and also a frame
control code. The slave returns an error code in the event of an error.
Further information on protocols can be found in the appendix.
Only the following MODBUS
®
operation codes may be processed by the 40 and 50 series
basic units:
Function codes (Hex) Description
01 or 02 Read n bits
03 or 04 Read n words
05 Write a bit
06 Write a word
07 Rapid read of 8 bits
08 Diagnosis/initialization
0F Write n bits
10 Write n words
The following codes are generated in the event of an error:
Error codes Description
01 Unknown function code
02 Address error
03 Data error
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