User Manual of EM730 Series Inverter 1.1.1.4 0x08: function code for diagnosis The Modbus function code 08 involves a series of tests to check the communication system between the client (master station) and server (slave station), or internal error statuses of the server. The test to be executed is defined by the sub-function code fields of two bytes in the request. The server makes responses properly. terminal unit to return the corresponding data through the data field in normal response. Copy the function codes and sub-function codes.
Some diagnoses will enable the remote Under normal circumstances, when the diagnosis function is sent to the remote terminal unit, the user program in this remote terminal unit will not be affected. The user logic cannot be accessed by diagnosis, such as: discrete magnitude and register. The error counter in the remote terminal unit can be remotely reset by applying some functions. The main diagnosis function used by our company is line diagnosis (0000), which is used to test the normal communication between the host and slave. The normal response to a request to return query data is to return the same data. At the same time, the function codes and sub-function codes are also copied.
Request PDU Response PDU Error PDU Sub-function code 375 Function code 1 byte 0x08 Sub-function code 2 bytes 0x0000 - 0xFFFF Data 2 bytes 0x0000 - 0xFFFF Function code 1 byte 0x08 Sub-function code 2 bytes 0x0000 - 0xFFFF Data 2 bytes 0x0000 - 0xFFFF Error code 1 byte 0x88 Exception code 1 byte See Table 4-33