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MODBUS_RTU_SET_RTS(3)          Libmodbus Manual          MODBUS_RTU_SET_RTS(3)


NAME

       modbus_rtu_set_rts - set the RTS mode in RTU


SYNOPSIS

       int modbus_rtu_set_rts(modbus_t *ctx, int mode)


DESCRIPTION

       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 1ms, then another ioctl call is made with the RTS
       flag disabled and again a delay of 1ms occurs. The MODBUS_RTU_RTS_DOWN
       mode applies the same procedure but with an inversed RTS flag.

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


RETURN VALUE

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


ERRORS

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


EXAMPLE

           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);


SEE ALSO

       modbus_rtu_get_rts(3)


AUTHORS

       The libmodbus documentation was written by Stephane Raimbault
       <stephane.raimbault@gmail.com[1]>


NOTES

        1. stephane.raimbault@gmail.com
           mailto:stephane.raimbault@gmail.com

libmodbus 3.1.0                   10/06/2013             MODBUS_RTU_SET_RTS(3)

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