ZyXEL Communications U-336E, User Manual

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Basic Modem Operation 13
3
Basic Modem Operation
This chapter covers the basic commands and techniques involved in
modem operation. In many cases, this is the only information you
will need in order to get up and running with communication
software, and to start making connections with your modem.
Understanding AT Commands
The U-336E communicates asynchronously with computers using
AT commands. AT commands are used to configure and control
your modem. Commands are usually sent to the modem by way of
communication software, but can also be entered manually by the
user with the computer keyboard.
Command statements must be written in a specific form in order for
your modem to recognize them. A command statement always
begins with the letters AT or at. It is then followed by one or more
commands and the <Enter> key.
AT commands can only be issued when your modem is in
“command mode” or “off-line.”
Once your modem has established a connection with another
modem it is said to be “on-line” or in “data mode.” In this mode,
the characters sent to your modem by your computer are
transmitted to the remote modem rather than being interpreted by
your modem as commands.
Using the Windows 95 Hyper Terminal Program
In order to issue an AT command statement, you first need to run a
communication program such as the Microsoft Windows “Hyper