1. When a Modbus/TCP client established a new connection to
the MEP card, output process data status initially is set invalid
at the MEP. The output data status changes to valid, as soon as
all parameters at output process data list are written at least
once. The output data status then remains valid, until the TCP
connection is closed or terminated.
2. Special Register Addresses mentioned above, only can be used
without any offset. Example: It is not allowed to use address
0x7FF2 for accessing second output process data item.
9.3 Exception Codes
With Modbus/TCP, in error cases, the MEP card returns Exception Codes at the
Modbus response telegram. The Exception Codes are listed in the following ta-
ble:
Exception Code Name Meaning/Possible Causes
1 Illegal function
Unknown Function Code, transaction contained a Modbus
Function Code not supported by the MEP card.
2 Illegal data address
● Access to unknown address
● Error occurred while Function Code 43 transaction
3 Illegal data value
● Invalid read/write length value at Modbus transaction
● Malformed request telegram
● Invalid object ID at Function Code 43 transaction
4
Server device fail-
ure
Read / Write access failed
Tab. 9-3:
Exception codes
Multi-Ethernet Card Bosch Rexroth AG
Modbus/TCP
DOK-RCON0*-XFCX610*MUL-IT02-EN-P
47/61
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