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Appendix
APPENDIX H
Introduction to MultiTech Escape Methods
You may sometimes find it necessary to issue AT commands to your modem, while you are online with a
remote modem, without disconnecting the call. If so, you will want to take advantage of escape methods that
allow you to change the modem's mode of operation from online mode to command mode. After you issue
your AT commands, you may return to online mode, but typically most users escape so that they can hang up
a modem upon completion of a call.
Our modems offer two escape methods: in-band and out-of-band. Both incorporate Time Independent
Escape Sequence (TIES) methodology. An escape sequence is a pattern or sequence that the modem
recognizes as its signal to shift from online mode to command mode. "Time independent" means that the
modem recognizes the escape sequence without a prefixed and/or suffixed delay.
In an in-band escape, the modem recognizes the escape sequence as a pattern sent to it as part of the data
stream or band (hence its name).
In an out-of-band escape, the escape sequence is a pattern that cannot and does not occur in the data
stream.
Our in-band escape method is +++AT<CR>
Our out-of-band escape method is <BREAK>AT<CR>
A break signal cannot be sent as part of a data file; instead it is sent by a direct program command to the
UART used by the computer.
The break signal is defined as either the transmission of binary 0 for a minimum of 10 bits; or as a minimum
interval of 135 milliseconds as established in the ITU-T X.28 standard. Routines in high level languages, and
keys on most computers, can send the break signal for fixed intervals.
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