Modems - AT&T MERLIN LEGEND Data Manual

Data Communications Hardware

Modems

Hardware
See System Reference for information
on the MFM and GPA.
A modem is used at an analog data station to place or answer data calls.
Modems convert outgoing digital signals from the data terminal into analog
signals for transmission, and convert incoming analog signals to digital signals
for the data terminal.
Since you can connect different types of modems to the system, specific
modem hardware is not discussed in this' book. Modems also provide a variety
of features in addition to the basic features listed below. Modems used in
modem pools, however, must have the following features:
full-duplex operation
support of 10-bit code (start, 8 data bits, stop)
RS-232 asynchronous interface
data rates of 300, 1200, 2400, 4800, and 9600 bps
dual-tone multi-frequency (DTMF) dialing through the RS-232 interface
ability to turn on or maintain the Clear-to-Send indicator when it is ready to
receive ASCII dialing sequences from the data module in response to a
Data-Terminal-Ready signal from the data module
ability to keep the Data-Set-Ready lead on (and not turn it off) during
transition from the interactive dialing mode to the data mode
ability to terminate a data call or dialing sequence when the data module
turns off its Data-Terminal-Ready lead
ability to turn off the Data-Set-Ready or Receive-Line-Signal-Detect lead for a
minimum of 50 ms when hanging up at the termination of a data call
ability to turn on the Ring indicator lead for at least 100 ms in the presence of
an incoming analog call
support of Electronic Industries Association (EIA) signals Cl and CI2 if the
modem is multispeed
AT&T model 2224G (PEC 2224-CEO for stand-alone, PEC 2224-GED for rack-
mounting arrangement) is recommended for modem pools.
To use a modem with an MLX telephone, install a Multi-Function Module (MFM)
in the telephone to provide a tip/ring (T/R) interface for the modem. The modem
connects directly to the MFM. You use the data terminal keyboard to dial data
calls and use the telephone dialpad to dial voice calls. Each device operates
independently, and features are assigned to each device independently.
To use a modem with an analog multiline telephone, install a General Purpose
Adapter (GPA) to provide a T/R interface. You use the telephone dialpad to dial
data and voice calls. Features assigned to the telephone are also assigned to
the analog data station.
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Modems