Automatic answering is enabled when the value in register S0 is set to between 1 and 255. The default value of zero disables the facility. The value held in S0 controls the number of rings the modem receives before answering the incoming call. For example:

ATS0=3 <Return>

instructs the modem to wait for three rings before going into answer mode.

Having gone off hook in answer mode, the modem sends an answer tone and negotiates a connection at the highest possible speed. If no common line speed exists or an originate carrier from the remote system is not detected within the period specified in register S7, no connection is made, the modem hangs up and returns to local mode.

Note: The factory default setting of &D2 inhibits auto-answer if the modem control signal DTR (Data Terminal Ready) is off.

Alternatively the "A" command can be used to instruct the modem to answer. The modem first checks that either RING is detected or that the telephone handset is in use (on a previously established voice call) before going off hook and sending an answer tone. If the handset is not in use on the line or the phone is not ringing the modem returns the ERROR message.

Additionally, the -SDR command can be used to enable Distinctive Ring. This is a facility provided by certain telephone systems whereby different telephone numbers are assigned to one physical line. When one of these numbers is dialled, the telephone system produces a Distinctive Ring associated with the number dialled. The modem can detect these ring signals and output a special RING# message where # represents a number corresponding to the type of ring signal received. See the AT Commands chapter for further details.

By default the escape code character is the "+" symbol (ASCII 43). After issuing the escape sequence "+++" the modem switches to command mode. However, it is possible that the "+" character may cause problems on some bulletin board systems. For this reason the character may be redefined by changing the value in register S2.