modbus_report_slave_id - returns a description of the controller
The modbus_report_slave_id() function shall send a request to the controller to obtain a description of the controller.
The response stored in
- the slave ID, this unique ID is in reality not unique at all so it's not possible to depend on it to know how the information are packed in the response.
- the run indicator status (0x00 = OFF, 0xFF = ON)
- additional data specific to each controller. For example, libmodbus returns the version of the library as a string.
The function writes at most
max_dest bytes from the response to
you must ensure that
dest is large enough.
The function shall return the number of read data if successful.
If the output was truncated due to the
max_dest limit then the return value is
the number of bytes which would have been written to
dest if enough space had
been available. Thus, a return value greater than
max_dest means that the
response data was truncated.
Otherwise it shall return -1 and set errno.