AT&T Callmaster Series Reference Manual page 719

The 3270 Data Module provides a Category A coaxial DCE interface for connection to 3270-type
data terminals or a cluster controller. It also provides a DCP interface for connection to the digital
switch.
The 3270 Data Module is available in the following three models:
3270T (Terminal)Connects to a Category A 3270-type terminal, such as the IBM 3278
Information Delivery System. The 3270T Data Module must connect through the switch
to a 3270C (Controller) Data Module.
3270A (Asynchronous)Provides the same function as the 3270T Data Module. It also
allows the 3270-type terminal to emulate a DEC VT100 or AT&T's Information Systems
asynchronous terminal.
3270C (Controller)Connects an IBM 3274 or 3276 cluster controller to the switch. A
3270C Data Module (See Figure 2) can contain as many as eight ports.
3270 Data Module
3270 Data Module
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