IBM RS/6000 44P Series 270, Service Manual, Page: 316 / 346

The modem command &Dn (where ’n’ is a number) generally sets the modem
response to the data terminal ready (DTR) signal from the server’s serial port. The
desired response is that the modem will hold a connection while DTR is enabled, and
drop the connection when DTR is released. This is the mechanism by which the server
hangs up on a connection under normal conditions.
Consult your modem manual for its specific response scheme for the &Dn command.
Two strategies are available for dealing with the modem’s response to DTR:
v Recovery
v Prevention
Before you use one of these strategies, determine if your server’s modem is set up
properly to respond to DTR.
With the remote terminal connected to serial port 1 and defined as the primary console
device, there are two tests you can perform:
1. Will the modem drop the connection after the
System initialization complete
message displays at the remote terminal?
If yes, the modem is set up correctly.
If no, try another &Dn setting for your server’s modem. See your modem manual for
this information. The &Dn command appears in three places each in three of the
sample modem configuration files:
v modem_f.cfg
v modem_f0.cfg
v modem_f1.cfg
2. Will the server’s modem disconnect when the power drops? You can make this
observation at the remote terminal by commanding your server to shutdown and
power off. (The AIX command
shutdown -F will do this.) Watch for the message NO
CARRIER
on your remote terminal.
If Yes, this is the correct response. The modem is set up correctly.
If No, try another &Dn setting for your server’s modem. See your model manual for
this information. The &Dn command appears in three places each in three of the
sample modem configuration.
If you are using modem_z.cfg or modem_z0.cfg, you cannot control DTR response. If
your remote terminal does not disconnect after logging off, you must command the
remote terminal emulator to hang up. This then breaks the connection.
Recovery Strategy
The recovery strategy consists of making two calls to establish a remote session. This
is the easiest solution to implement, and allows more freedom for configuring your
server’s serial ports.
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Service Guide