User Manual of EM760 High-Performance Inverter ● If the slave station receives a request without communication error but cannot process the request (e.g. a request to read the non-existent register), the slave station will return an exception response and the master station will be informed of the actual error. The exception response message has two fields different from those of the normal response: ● Function code field: In the normal response, the slave station copies the function code ofthe original request in the corresponding function code field. The MSB values of all function codes are 0. In the exception response, the MSB ofthe function code is set to 1 by the slave station.
That is, the exception response function code = normal response function code + 0x80 . ● Data field: The slave station can return the data from the data field in the normal response and exception code in the exception response. The defined exception codes are detailed in the table below. Table 10-4 Definitions of Exception Codes 10.4Protocol Description 10.4.1 Definition of inter-frame and intra-frame time interval A complete MODBUS message contains not only the necessary data units, but also the starting and ending tags. Thus, as shown in Fig. 10-2 or Fig. 10-4, the idle level with a transmission time of 3.5 characters or more is defined as the starting and ending tag.
If there is an idle level with a transmission time of more than 1.5 characters during message transmission, the transmission will be deemed exceptional. Specific starting/ending and exception intervals are related to the baud rate, as detailed in Table 6-27. Ifthe baud rate is 9600bps and the sampling period is 1ms, the starting and ending time interval is the idle level of 4ms or more (3.5Ч10/9600=3.64≈4), and the exceptional data interval is the idle level in which the interval of data bits of one frame is greater than or equal to 2ms (1.5Ч10/9600=1.56≈2) and less than 4m (the idle level of normal data bits is less than or equal to 1ms).
272 Exception code Item Meaning 01H Illegal function The function code received by the slave station (inverter) is beyond the configured range (see11.3.3 Function codes). 02H Illegal data address The data address received by the slave station (inverter) is not allowed. In particular, the combination of the start address of the register and the transmission length is invalid (see11.3.4 Register address distribution). 03H Illegal data frame The slave station (inverter) has detected the incorrect query data frame length or CRC check. 04H Slave protection When the slave station (inverter) tries to execute a requested operation, an unrecoverable error occurs.
This maybe caused by the logic error, failure to write to the EEPROM, etc. 05H Data over-range The data received by the slave station (inverter) is not between the minimum and maximum values of the corresponding register. 06H Parameter read-only The current register is read-only and cannot be written. 07H Unchangeable parameter in running When the inverter is in the running status, the current register cannot be written. If necessary, please shut down the inverter. 08H Parameter protection by password The current register is protected by a password.