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2.4
Call Termination
There are several methods by which you can terminate a call, or simply stated, hang up:
1.
Command Mode Control. It is possible to enter command mode while remaining online by entering an
escape sequence ( +++AT<CR> in most cases). From command mode, you can return to the online state
by typing ATO , or you can terminate the call by using the H command. Typing ATH will hang up the line
(bring it on-hook). So the command to hang up a call is three plus signs followed by ATH .
2.
DTR Control. If DTR (Data Terminal Ready) is turned off for 50 milliseconds or more, a disconnect will
occur. This is probably the most common method used by computer systems at the autoanswer end of
the line to cause the calling modem to disconnect after logoff procedures.
3.
Loss of Carrier. Once a data connection has been established, the modem will disconnect if a loss of
carrier occurs for 700 milliseconds (0.7 seconds) or longer. This time can be configured with register S10
for any time from 0 to 25.5 seconds (in 100 mSec increments). Note that one cause of carrier loss would
be if one of the modems were to disconnect normally. S10 works for speeds of 2400 bps or below. S10
has no effect at connections above 2400 bps.
4.
Abort Timer. Answer Mode: When OH (Off Hook) comes on, the called modem starts a 45 second timer
and waits for a carrier signal from the originating modem. If a 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 the 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 45-second wait period to any other
value from 1 second up to 254 seconds by reconfiguring register S7 (see Chapter 4).
5.
Inactivity Timer. Causes the modem to disconnect if no data is being transmitted or received for a
certain period of time. The timer is reset anytime a character passes through the serial port in either a
send or receive direction. This function is controlled by register S30 . The inactivity timer can be disabled
by setting S30 to 0, which is the factory default setting, or set to time out after number of minutes selected
by register S30 .
Chapter 2 - Dialing and Answering
19
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