ABB 07CR41 Operating Manual page 101

Advant Controller AC 31 / Issued: 01.99
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The MODBUS frames transmitted by the master contain the following information:
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- 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
basic units:
Function codes (Hex)
01 or 02
03 or 04
05
06
07
08
0F
10
The following codes are generated in the event of an error:
Error codes
01
02
03
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operation codes may be processed by the 40 and 50 series
Description
Read n bits
Read n words
Write a bit
Write a word
Rapid read of 8 bits
Diagnosis/initialization
Write n bits
Write n words
Description
Unknown function code
Address error
Data error
6 – 7 Communication
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