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CHAPTER 4: Manual Dial and Automatic Answer
4.3 Automatic Leased Line Restoral Operation
(336+ Only)
When the Series II Modem 336+ (MD1640A) is in Dial Backup mode, it
periodically checks the leased line to see if it's operational and tries to
restore the leased line if possible. S-Register S18 determines how often
restoral attempts occur. The default for S18 is 30 minutes, and can be
set in one minute increments from 10 to 255 minutes. Setting the
restoral attempts under 10 minutes causes excessive breaks in the
dial-up operation.
Note: Both local and remote modems must have S-Register S18 set
identically. Refer to Chapter 6 for more information on S-Register S18.
4.4 Manual Dial Backup Call Termination (336+ Only)
With your Series II Modem 336+ (MD1640A) in leased line mode (DIP-
Switch #10 in the DOWN position) and with dial backup operation in
process, there are two ways to manually terminate the dial backup call
(other than automatic leased line restoral). In each case, you will try to
establish the leased line connection because it is back in operating
condition. The methods of dial backup call termination are:
1) Manual Control. The "Voice/Data" switch can be used to change
from a dial back line to leased line by toggling down once. When
that is done, the Modem tries the leased line connection, and, if it
is good, the modem disconnects the dial back call and establishes
a leased line connection.
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 toggling off procedures.
4.5 Dial Backup and Leased Line Restoral (336+ Only)
The dialing associated with the Series II Modem 336+ (MD1640A) when
it's in "leased line with dial-back" mode, involves placing a call from the
originating modem due to a leased line failure.