AT&T MERLIN LEGEND Release 4.0 Feature Reference page 358

Feature Reference
Although each MLX extension jack used to connect an MLX telephone is
assigned only one logical ID, the system automatically assigns two extension
numbers, one for the MLX telephone and one for the device connected to the
MFM. Both extension numbers are assigned to the jack whether or not an MFM
is connected. Since a separate extension number is assigned, features and
trunk access can be assigned to the MFM independently of the MLX telephone.
See "System Numbering" for details on specific extension numbers assigned.
The ringing patterns for devices connected to an MFM are similar to those of an
MLX telephone rather than a single-line telephone ring for inside calls: two rings
for outside calls, and a ring and two beeps for priority ring or transfer return.
A switch on the MFM can be set for one of the following operations:
Tip/ring interface
Supplemental Alert Adapter (SAA)
Tip/Ring Interface
When the MFM is set for tip/ring interface operation, only dual-tone
multifrequency (DTMF) tip/ring devices can be used to make and/or receive
inside and outside calls. The following types of DTMF devices can be used:
Single-line telephones
Modems
Fax machines
Credit card verification terminals
Cordless single-line telephones
Speakerphones that emulate a tip/ring device
Answering machines
Supplemental Alert Adapter
When the MFM is set for SAA operation, an external alert that requires a 48-VDC
contact closure can be connected.
If the external alert is used to supplement the ringing for both inside and outside
calls, the MFM should be assigned (through centralized telephone
programming) as a Primary Individual Coverage receiver with the ringing option
of Immediate Ring. The MLX telephone can use Coverage On/Off to activate the
alert. In addition, by specifying that both inside and outside calls or only outside
calls are covered with the coverage arrangement, the sender (in this case the
MLX telephone user) can specify that the device (the receiver) rings for both
inside and outside calls or only for outside calls.
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Multi-Function Module