Basic Modem Operation; Understanding At Commands - ZyXEL Communications U-336S User Manual

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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-336S/SA 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.
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