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Chapter 4 - Manual Dial and Automatic Answer
4.7 Call Termination
There are a number of ways to terminate a call, or simply stated, hang up. They are:
1) Command Mode Control. To terminate a call by Command Mode, enter +++ATH then
RETURN; or, send a BREAK signal followed by ATH and a RETURN.
2) DTR Control. If DTR (Data Terminal Ready) is turned off for 50 milliseconds or more, a
disconnect occurs. This is probably the most common method used by computer systems at the
automatic answer end of the line to cause the answering modem to disconnect after logging off
procedures.
3) Loss of Carrier. After a data connection is established, the modem disconnects if a loss of
carrier occurs for 700 milliseconds (0.7 seconds) or more. Note that one cause of carrier loss
would be if one of the modems disconnect normally.
4) Abort Timer.
Answer Mode: When OH (Off Hook) comes on, the called modem starts a forty-five-second
timer and waits for a carrier signal from the originating modem. If carrier is not detected within
this period, the modem disconnects (hangs up) and is ready for another call.
Originate Mode: The abort timer functions the same as in answer mode, except that the timer
begins after the modem has completed dialing, instead of when it first goes off hook. It is possible
to change this forty-five second wait period to any other value (from 0 seconds up to 255
seconds), or to disable the timer completely by re-configuring S-Register S7 (see Chapter 6).
5) Inactivity Timer. Causes the modem to disconnect if no data is transmitted or received for a
specified time. The timer is restored any time a character is passed through the serial port in
either a send or receive state. This timer runs in both normal or reliable connections and is
controlled by S-Register S30. The Inactivity Timer can be disabled by setting S30 to 0, which is
the factory default setting.