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10.9 Exceptions and Troubleshooting
Although by no means exhaustive, Table 6 provides some possible causes behind
some of the most common errors experienced when using the Modbus TCP/IP
interface.
Table 6: Troubleshooting Reference
Problem Possible Cause
Register addressing is off by 1 Refer to Section 10.3 for Modbus/drive mapping
Modbus TCP/IP client cannot establish
communication with the ETH-100
• Ensure at least one of the connected drives is powered on
• Check that the drive and Ethernet communication cables
are fully seated into their respective communication ports
• Check the Ethernet communication parameters (IP
address, etc.)
Drive does not respond to network
commands / frequency command
• Check drive’s frequency mode and command mode
selection parameters
• Where applicable, confirm the values of bits #14 and #15
of communication command word
• Confirm that communication frequency command value is
between lower limit and upper limit frequencies
ILLEGAL FUNCTION exception
(Modbus exception code 01)
The indicated Modbus function is not supported: refer to section
10.2 for a list of supported functions
ILLEGAL DATA ADDRESS exception
(Modbus exception code 02)
The targeted drive register (or one in a group of targeted
registers) does not exist: check the drive’s supported register
list
ILLEGAL DATA VALUE exception
(Modbus exception code 03)
The value written was rejected by the drive as invalid: check the
value and drive setting range
NEGATIVE ACKNOWLEDGE exception
(Modbus exception code 07)
• An attempt was made to write to a drive register while the
drive was running that does not accept writes while the
drive is running
• An attempt was made to write to a read-only register
• Confirm that the drive communication cable is fully seated
into the drive’s and ETH-100’s communication ports
• Confirm that the drive communication cable is not routed
near the drive’s input power or motor wiring or any other
electrical noise-producing cables or equipment
GATEWAY PATH UNAVAILABLE
exception (Modbus exception code 0A)
Unit Identifier (UI) was invalid: UI must be 1 ∼ 3
GATEWAY TARGET DEVICE FAILED TO
RESPOND exception
(Modbus exception code 0B)
The targeted drive is not online or failed to respond:
• Confirm that the targeted drive is powered-on
• Confirm that the drive communication cable is fully seated
into the drive’s and ETH-100’s communication ports
• Confirm that the drive communication cable is not routed
near the drive’s input power or motor wiring or any other
electrical noise-producing cables or equipment
