11
Exception Responses:
Except for broadcast messages, the AC drive is been expected to return a normal response
after receiving command messages from the master device. The following depicts the
conditions that no normal response is replied to the master device.
The AC drive does not receive the messages due to a communication error; thus, the AC
drive has no response. The master device will eventually process a timeout condition.
The AC drive receives the messages without a communication error, but cannot handle it,
an exception response will return to the master device. In the exception response, the most
significant bit of the original command code is set to 1, and an exception code explains the
condition that caused the exception is returned. An example of exception response of
command code 06H and exception code 02H:
STX ‘:’ 3AH
‘0’ 30H ADDRESS 1
ADDRESS 0
‘1’ 31H
FUNCTION
(CMD) 1
‘8’ 38H
FUNCTION
(CMD) 0
‘6’ 36H
‘0’ 30H EXCEPTION
CODE
‘2’ 32H
‘7’ 43H LRC CHK 1
LRC CHK 0
‘7’ 46H
CR 0DH END 1
END 0
LF 0AH
The explanation of exception codes:
Exception codes: Explanation
01
Illegal command code:
The command code received in the command message is not
available for the AC drive.
02
Illegal data address:
The data address received in the command message is not available
for the AC drive.
03
Illegal data value:
The data value received in the command message is over range for
the AC drive.
04
Slave device failure:
The AC drive is unable to perform the requested action.
09 Check Sum Error: Check if the Check Sum is correct.
20
Watchdog Timer: The timer will reset to 0 after each valid MODBUS
communication message is received.
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