AT&D0 : ignore
transition of DTR status AT&D1 : switch
to command phase if DTR
OFF
*
AT&D2 : abort
connection if DTR OFF
AT&D3 : abort
connection and reinitialize if DTR
OFF
These commands are used to
set the response of the ISDN terminal adapter to
a transition of the control line DTR from ON to
OFF.
With the setting AT&D0,
the ISDN terminal adapter ignores the DTR
transition from ON to OFF.
With AT&D1, the
transition of the DTR control line from ON to OFF
has the following effects: If the ISDN terminal
adapter is in the command phase, the transition
has no effect. During the establishment of a
connection, the ON to OFF DTR transition aborts
the connection. If the ISDN terminal adapter is
in the transmission phase (i.e. with an existing
connection), it will switch to the command phase.
With AT&D2, the
transition of the DTR control line from ON to OFF
has the following effects: If the ISDN terminal
adapter is in the command phase, the transition
has no effect. During the establishment of a
connection, the ON to OFF DTR transition aborts
the connection. If the ISDN terminal adapter is
in the transmission phase (i.e. with an existing
connection), it will abort the connection and
switch to the command phase.
With AT&D3 the
ISDN terminal adapter's response is the same as
with AT&D2. In addition, the ISDN
terminal adapter is reinitialized by the DTR
transition from ON to OFF (see also ATZ
and AT&Y).
With AT&D2 and AT&D3
as well as DTR = OFF, the ISDN terminal adapter
does not return a RING for incoming calls.
Automatic call answering is not possible until
after the DTR transition from OFF to ON. A RING
message with subsequent call answering can be
enabled despite DTR = OFF by setting bit 7
in register S28.
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