modbus_rtu_set_rts - set the RTS mode in RTU

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

libmodbus v3.1.6                                   12/09/2019                              MODBUS_RTU_SET_RTS(3)

       The modbus_rtu_set_rts() function shall set the Request To Send mode to communicate on a RS485 serial
       bus. By default, the mode is set to MODBUS_RTU_RTS_NONE and no signal is issued before writing data on
       the wire.

       To enable the RTS mode, the values MODBUS_RTU_RTS_UP or MODBUS_RTU_RTS_DOWN must be used, these modes
       enable the RTS mode and set the polarity at the same time. When MODBUS_RTU_RTS_UP is used, an ioctl call
       is made with RTS flag enabled then data is written on the bus after a delay of 1 ms, then another ioctl
       call is made with the RTS flag disabled and again a delay of 1 ms occurs. The MODBUS_RTU_RTS_DOWN mode
       applies the same procedure but with an inverted RTS flag.

       This function can only be used with a context using a RTU backend.

EINVAL
           The libmodbus backend isn’t RTU or the mode given in argument is invalid.

EnabletheRTSmodewithpositivepolarity.

           modbus_t *ctx;
           uint16_t tab_reg[10];

           ctx = modbus_new_rtu("/dev/ttyS0", 115200, 'N', 8, 1);
           modbus_set_slave(ctx, 1);
           modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485);
           modbus_rtu_set_rts(ctx, MODBUS_RTU_RTS_UP);

           if (modbus_connect(ctx) == -1) {
               fprintf(stderr, "Connexion failed: %s\n", modbus_strerror(errno));
               modbus_free(ctx);
               return -1;
           }

           rc = modbus_read_registers(ctx, 0, 7, tab_reg);
           if (rc == -1) {
               fprintf(stderr, "%s\n", modbus_strerror(errno));
               return -1;
           }

           modbus_close(ctx);
           modbus_free(ctx);

       modbus_rtu_set_rts - set the RTS mode in RTU

       The function shall return 0 if successful. Otherwise it shall return -1 and set errno to one of the
       values defined below.

modbus_rtu_get_rts(3)

intmodbus_rtu_set_rts(modbus_t*ctx,intmode)