Telebit T3000 Reference Manual page 90

&D1 The modem enters command mode when a
filtered ON-to-OFF transition of DTR is detected.
(Filter time is defined by the 825 register.) Auto
answer ignores DTR.
&D2 The modem disconnects a call in progress, enters
command mode, and disables auto-answer when
the DTR signal goes from ON to OFF. Auto
answer is enabled when the DTR signal goes ON
and returns to an active state.
&D3 The modem resets and enters command mode
when the DTR signal goes from ON to OFF. This
causes the modem to recall the current user
configuration parameters from nonvolatile
memory.
&F(n) Load Factory Defaults
Range: 0-5, 8-13, 32-34
See also: S254, S255
The &F command loads the ROM-based factory
defaults into the active configuration except for
registers S254 and S255.
&F Same as &FO.
&FO TTY (factory default)-Load configuration
according to the 8254 register. Used with most
asynchronous terminals or PCs emulating
asynchronous terminal operation.
&F1 Unattended Answer Mode. Used with most
asynchronous Front End Processor (FEP) host
ports operating at a fixed interface speed of 9600
bps.
AT Command Descriptions 5-15