WEG MVW3000 A0040 V023, User Manual

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9-36 | MVW3000
9
Communication Networks
9-36 | MVW3000
In this example, the object values were not represented in hexadecimal, but using the corresponding ASCII
characters. For the object 00, for instance, the value ‘WEG’ was transmitted as being three ASCII characters that
in hexadecimal have the values 57h (W), 45h (E) and 47h (G).
9.3.4 ModBus RTU Communication Error
Errors may occur in telegram transmission through the network, or in the contents of the received telegrams.
According to the type of error, the inverter may or may not send a response to the master:
When the master sends a message to an inverter configured at a specific network address, the inverter will not
respond to the master if the following occurs:
„
Parity bit error.
„
CRC error.
„
Timeout between transmitted bytes (3.5 times the transmission time of a 11 bit word).
In the case of a successful reception, during the telegram processing the inverter may detect problems, and send
an error message, indicating the type of problem found:
„
Invalid function (error code = 1): the requested function has not been implemented for the inverter.
„
Invalid data address (error code = 2): the data address (register or bit) does not exist.
Data value invalid (error code = 3): this error occurs in the following conditions:
„
Value is out of the permitted range.
„
Writing in data that cannot be changed (read-only register, or one that does not allow changing with enabled
inverter, or Status Word bits.
„
Writing in a Control Word function that has not been enabled via serial interface.
Error Messages
When any error occurs in the message content (not during the data transfer), the slave must return a message
indicating the error type that occurred. The errors that may occur in the MVW3000 during the message processing
are invalid function (code 01), invalid data address (code 02), and invalid data value (code 03) errors.
The messages sent by the slave have following structure:
Table 9.29: Telegram structure
Response (Slave)
Slave address
Function code
(with most significant bit to 1)
Error code
CRC-
CRC+
Example: The master requests the slave at address 1 to write in the parameter 89 (inexistent parameter):