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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 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
-------
.Enable the RTS mode with positive polarity
[source,c]
-------------------
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
--------
linkmb:modbus_rtu_get_rts[3]
AUTHORS
-------
The libmodbus documentation was written by Stéphane Raimbault
<stephane.raimbault@gmail.com>
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