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Selecting Speeds
The following section describes how to select line and terminal speeds for your modem.
Terminal Speeds
Your modem has the ability to communicate with your computer at various speeds. The modem
offers two speed modes: variable speed mode and constant speed mode.
Constant speed mode forces your modem to maintain the terminal speed that was selected when
you dialed another modem, even if the connection speed made with the other modem does not
match the terminal speed of your modem and computer.
For example, if your modem connected to another modem at 2400 bps and its terminal speed is
9600 bps, the modem will maintain its terminal speed at 9600 bps. Because of this, you must
select flow control between the modem and your computer. To select constant speed mode:
• Type: AT\N0 <E>
For more details on constant speed mode and flow controls, see the Command Descriptions
chapter for a discussion of the \N, B and &K commands. + Some computers cannot cope with
receiving data at speeds above 19,200 bps. If you wish to run at high speeds, you should install
a COM port that has a 16550 chip in place of your regular COM port. The 16550 chip allows
your computer to accept data at very high speeds when used with suitable drivers and software.
Variable speed mode allows your modem to automatically adjust its terminal speed to match the
line speed. For example, if your modem connects to another modem at 4800 bps and its terminal
speed is 9600 bps, the modem will automatically change its terminal speed to 4800 bps (and,
thus, you or your software would have to change the speed of your computer to 4800 bps).
If you have variable speed mode and B0, B1, B2 or B9 selected, the modem will attempt to
connect at a speed to match the terminal speed.
At 300 bps, select B0 or B2 for V.21, or B1 for Bell 103. At 1200 bps, select B0 for V.23, B1 for
Bell 212A, or B2 for V.22.
Variable speed mode may be selected by:
• Type: AT\N1 <E>
For more details about the variable speed mode, see the \N and B commands in the Command
Descriptions chapter of this guide.