NAME

       modbus_report_slave_id - returns a description of the controller

SYNOPSIS

       int modbus_report_slave_id(modbus_t *ctx, int max_dest, uint8_t *dest);

DESCRIPTION

       The modbus_report_slave_id() function shall send a request to the controller to obtain a
       description of the controller.

       The response stored in dest contains:

       •   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 dest so you must ensure
       that dest is large enough.

RETURN VALUE

       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.

EXAMPLE

           uint8_t tab_bytes[MODBUS_MAX_PDU_LENGTH];

           ...

           rc = modbus_report_slave_id(ctx, MODBUS_MAX_PDU_LENGTH, tab_bytes);
           if (rc > 1) {
               printf("Run Status Indicator: %s\n", tab_bytes[1] ? "ON" : "OFF");
           }

AUTHORS

       The libmodbus documentation was written by Stéphane Raimbault
       <stephane.raimbault@gmail.com>