12.2.3 Protocol Functions
Supported functions
The main function of Modbus is to read and to write parameters. Different
function codes decide different operation requests. Modbus functions man‐
aged by Fv and their limits are shown in table below.
Function
code
Meaning Broadcast Maximum value of N
3=0x03 Read N register parameters NO 16 characters in maximum
6=0x06 Rewrite a register with information stored even after power off YES –
8=0x08 Loop test NO –
16=0x10 Rewrite N registers with information stored even after power off YES 16 characters in maximum
23=0x17 Read from and write to N registers NO 16 characters in maximum
Tab. 12-2: Modbus functions managed by Fv and their limits
“Read” and “Write” are considered from the prospect of the mas‐
ter station.
If the device fails to act upon the request, it responds with a fault code and
exception code. The fault code is the function code plus 0x80. An example of
exception code is shown in table below.
Fault
code
Meaning Possible reason
1 Password locked User password locked
2 Function code fault Function code is not 03, 06, 08, 16, 23
3 Invalid address Undefined address
4 Invalid data Data exceeds limit
5 Parameters can not be modified in run mode Frequency converter is in run mode
6 Read only Not allowed to write in read only parameters
7 Invalid operation
Function code does not support write via external computer or mul‐
tiple write
8 CRC check failure Data fault or discontinuous frame
9 EEPROM read/write fault EEPROM write does not finish
Tab. 12-3: Fault codes_meanings_reasons
DOK-RCON02-FV*********-IB08-EN-P Bosch Rexroth AG 219/259
Rexroth Frequency Converter Fv
Communication Protocols
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