ADTRAN 3000 - Manual (Page 103)

Appendix A. AT Commands and S-Registers
61203153L2-20 Express 3000 User Manual A-5
Carrier Detect (CD) Control Line Options
Command Function
&C0 CD forced on.
&C1 CD normal.
&C2 CD off with local disconnect (LOCD).
&C3 CD off with link down.
Data Terminal Ready
(DTR Control Line Options)
Command Function
&D0 Ignore DTR.
&D1 DTR off forces command.
&D2 Idle when off. DTR off forces idle. (On allows auto answer.)