This configuring is normally done by your communications program
such as wvdial. It may do much of it without even letting you know what
it's done. In olden days it was done with the "stty" utility. If you
set something manually with stty, the communications program may
change the setting to something else so it's usually best to just let
the communications program handle it. See
What is stty ?
Flow Control for an explanation of
it. You should always use hardware flow control if possible. Your
communication program or "getty" should have an option for
setting it (and hopefully it's enabled by default). It needs to be
set both inside your modem (by an init string or default) and in the
device driver. Your communication program should set both of these
(if you configure it right).
If none of the above will fully enable hardware flow control. Then
you must do it yourself. For the modem, make sure that it's either
done by the init string or is on by default. If you need to tell the
device driver to do it is best done on startup by putting it in a file
that runs at boot-time. See the subsection
Boot-time Configuration You need to add the following to such
a file for each serial port (example is ttyS2) you want to enable
hardware flow control on:
stty -F /dev/ttyS2 crtscts
stty crtscts < /dev/ttyS2
If you want to see if flow control is enabled do the following: In
minicom (or the like) type AT&V (or ATI4 on 3Com modems) to see
how the modem is configured and look for &K3 (or &H1 on 3Com
modems) which means hardware flow control. Then without exiting the
communications program (such as minicom) see if the device driver
knows about it by typing: stty -F /dev/ttyS2 -a. Look for "crtscts"
(without a disabling minus sign). Remember that communication
programs change these settings so you may want to check them after you
have started up your communication program.
Besides flow control there is speed. See
What Speed Should I Use with My Modem. There's also are
parity and bits-per-byte settings. Normally the port is set by the
communications program at 8N1 (8-bits per byte, No parity, and 1 stop
bit). If you're running PPP then you must use 8N1. So if you get a
complaint that it's not 8-bit clean then it's likely not 8N1 like it
If the modem is not sending a CD signal and clocal is disabled
(stty shows -clocal) then a program may not be able to open the serial
port. If the port can't open, the program may just hang, waiting
(often in vain) for a CD signal from the modem. Actually, a skilled
programmer can write the program in such a way as to force the port to
open even when CD and -clocal say not to so it's not always a problem.
One way to avoid any possible problems is to send "AT&C" to the
modem so that CD from the modem will always be on. CD always-on is
fine for dial-out but for dial-in the CD signal is sometimes (but
rarely) used to detected an incoming call.
Minicom sets clocal automatically when it starts up so there is no
problem. But version 6.0.192 of Kermit hung when I set -clocal and
tried to "set line ...".
Here's a problem that existed prior to the year 2000 or thereabouts.
It's since been fixed. If -clocal is set and there is no CD signal,
then the "stty" command will hang and there is seemingly no way to set
clocal (except by running minicom). But minicom will restore -clocal
when it exits. One way to get out of this is to use minicom to send
the "AT&C" to the modem (to get the CD signal) and then exit
minicom with no reset so that the CD signal always remains on. Then
you may use stty again.
stty is something like setserial but it sets the speed (baud
rate), hardware flow control, and other parameters of a serial port.
Typing "stty -F /dev/ttyS2 -a" should show you how ttyS2 is
configured. Most of the stty settings are for things that you never
need to use with modems. Many of the setting are only needed for
Text-Terminals (and some are only needed for antique terminals of the
1970s). Your communication package should automatically set up the
several settings needed for modems. For this reason you normally don't
need to use stty so it's not covered much in this Modem-HOWTO. But
stty is sometimes useful for trouble-shooting. More is said about
stty in the Serial-HOWTO or Text-Terminal-HOWTO..