Black Box 3600 MODEM manual Answer Command a, On Hook H

Fax Operation

After dialing the specified number in fax mode, the modem generates 1100 Hz CNG tones in accordance with T.30 while trying to detect either CED (answer back tone) or the HDLC preamble of the first T.30 frame. The CNG tones cease after detecting either of these two signals. To allow proper interaction with manually answered fax stations, detection of CED is not required. After detecting 1650 Hz (i.e., the HDLC preamble of the first frame), the modem enters V.21 Channel 2 receive state with HDLC framing and returns a CONNECT result code. This is because dialing in fax mode (+FCLASS=1) implies an initial +FRH=3 command described in the “Fax Transmit and Receive Modes” section on pa ge9-7.

Answer Command A

The A command instructs the modem to answer the call. For fax operation, set the modem for Service Class 1 operation before the A command is issued; use the +FCLASS=1 command.

If the modem is in the online command state when an answer command is issued (e.g., a connection is already established), the modem returns an ERROR result code. Otherwise, it answers the call and generates a 2100 Hz CED (answer back) tone in accordance with T.30. The modem then enters V.21 Channel 2 transmit state with HDLC framing and returns a CONNECT result code. This is because answering a call in fax mode (+FCLASS=1) implies an initial +FTH=3 command described in the “Fax Transmit and Receive Modes” section on

page 9-7. To allow proper interaction with a manually originated fax call (in accordance with T.30), the modem does not require detection of CNG before generating CED or entering HDLC transmit mode.

If the DTE sends a character while executing the answer command and before CED is completed, the call is released and the modem will send the NO CARRIER result code.

On Hook H

In fax mode, the H command instructs the modem to stop any transmission and terminate the call by going on hook.

Modem 3600 9-5