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Modbus Errors
Modbus errors are typical protocol errors defined by fieldbus specification. The fieldbus error code shown is returned
to the PLC when the error condition occurs.
Code
Name
1
Illegal Function
2
Illegal Data Address
3
Illegal Data Value
4
Slave Device Fail
5
Acknowledge
6
Slave Device Busy
8
Memory Parity Error
10
Gatweay Path Unavailable
11
Gateway Target Fail
255
334183B
Cause
Request function is not supported. Use supported Modbus functions:
Exceeded maximum register count
of 121 registers.
No valid property mapped to the
requested Modbus register.
Write Holding Register(s) returns
set property error.
An active system error exists.
Unspecified
Solution
•
Read Holding Register
•
Write Holding Register
•
Write Multiple Holding Registers
Request 121 or fewer registers at a time.
Verify that the device has valid mapping.
See MBTCP Modbus Error for 4 red
flashes.
Verify that the end device is online.
Not implemented.
Not implemented.
Not implemented.
Not implemented.
Not implemented.
Not implemented.
Refer to system errors table.
Troubleshooting
9
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