modem doesn't answer
© December 2004 Tony Lawrence
(Mostly SCO related)
A modem that doesn't answer at all may not have any getty
running on it to assert DTR. If you don't see DTR, it isn't going
to answer. Power cycle the modem, disable the tty port, reenable
it. Don't have both the modem and non-modem ports enabled: disable
tty1a, enable tty1A. On systems very prone to losing this, I'll
even have a cron job that does this periodically; it won't
interfere with an existing connection (the disable will fail).
NO CARRIER usually means what it says: no dial tone. Modems need
working phone lines.
Don't use internal modems with Unix/Linux systems:
- External modems are only a few dollars more than internal.
- Internal modems take up a slot that you might need someday for
- Modems can get so confused that only shutting them off will
clear their problem. You don't want to shut off your server when
that happens, do you?
- If lightning comes down your phone line (it happens) and you
have an internal modem, your whole computer is likely to be fried.
With an external modem, you'll lose the modem, but probably not
- You can see what's going on with an external modem. You can see
when the modem is receiving, transmitting, handshaking- much easier
to diagnose problems.
- You can share an external modem between multiple computers
either manually or by an A/B box- again this facilitates testing
and is sometimes very convenient.
- When you upgrade your computer, swapping the modem is much
- When you finally get your cable modem, DSL line or T1 :-), you
might actually be able to sell that external modem, but used
internal cards are near worthless.
You can get more details on the actual conversation between
modems (or lack of conversation) by using "cu -x9" on systems that
use cu (which turns on diagnostic output). Or use "uutry -x9" with
a system name on systems with uucp.
On any old system, use Kermit.
The SCO modem manager doesn't work very well; see High speed modem
setup for the manual methods. The secret is forcing both the
modem and the serial port it is attached to set to run at a the
same fixed baud rate.
Related: What are
some common settings for my modem?
have a modem directly connected to a WY-60 terminal, but I don't
get any display of AT commands on the screen.
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