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.