MODBUS_RTU_SET_RTS(3) Libmodbus Manual MODBUS_RTU_SET_RTS(3)NAMEmodbus_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 ALSOmodbus_rtu_get_rts(3)AUTHORS
The libmodbus documentation was written by Stéphane 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)
