Boca FDSP34AI, Руководство по установке

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Extended commands were developed to provide greater functionality
and control over modem operations. Their format is the same as the
basic command except that an additional parameter is required
following the AT prefix and before the numerical parameter. This
additional parameter comes in three different forms:
the ampersand (&) character: extended AT command
the backslash (\) character: extended AT command for MNP
the percent (%) character: extended AT command for V.42/V.42bis
Examples: AT&V tells the modem to display (view) its current
configuration and user profile.
AT\G1 enables flow control. Flow control compensates for the difference
between the rate at which data reaches a device and the rate at which the
device processes and transmits.
AT%E1 tells the modem to monitor line quality and request a “retrain”
(adjustment) to the connection.
S-Registers
Modem command “language” also employs a set of indicators or
registers, which are various numerical values all with a standard “S”
prefix, hence S-Registers. To a large extent, the values defined in the S-
Registers regulate the operation of the modem and the function of some
commands in the AT command set.
Example: S-Register 6, or S6=n, defines the length of time the modem
will wait for a dial tone. In this case the acceptable range is 3-6 (in
seconds) with a default value of 5. With S6=3, the modem will wait three
seconds for a dial tone when going off-hook before dialing the first digit
of its telephone number.
Command Reference