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2-20
Data Channel Interface
There are eight selectable data channel interface types. Each interface type supports a particular
communications link between two data devices. The eight types are:
These standard data interfaces are created using both hardware and software selection devices.
The Data II, III, IV or UDC Channel module accepts four input control signals for transmission
to the opposite-end channel interface; these signals are passed out of the opposite-end channel
interface as four output control signals. Program plugs on the data channel modules select which
input control signals are multiplexed, and which output control signals are passed through the
channel interface.
The interface types selected through the supervisory port CRT identify which signals are being
selected, and allow the operator to force control signals on and off when required. Table 2-1
shows the program plug requirements for each interface type. Each item is described below:
DCE/DTE Program Plug (PP1)
This program plug determines whether the channel has a DCE (Data Communications Equip-
ment) inter-face, or a DTE (Data Terminal Equipment) interface. To communicate with a data
communications device (modem or multiplexer) the channel must have a DTE interface; to com-
municate with a data terminal device (CPU, CRT, printer, etc.) the channel must have a DCE in-
terface. The difference is simply in the designation of pins on the interface connector as inputs or
outputs for interface signals. For example, Transmit Data is an output of a DTE interface, but is
an input of a DCE interface. A DTE interface generates Request to Send as an output, and accepts
Data Carrier Detect as an input; a DCE interface generates Data Carrier Detect as an output and
accepts Request to Send as an input.
The DTE/DCE program plug places output and input signals on the proper interface connector
pins for the selected interface.
Control Signal Program Plug (PP2)
This program plug supports a selected interface type by providing special pathways between the
interface connector pins and the interface circuits of the Data Channel II, III, IV or UDC module.
Wires on the plugs select particular control signals to be transmitted to the opposite-end channel
interface as SEND Controls 1 through 4; RCV Controls 1-4 are selected to be passed to certain
pins of the interface by the control signal program plug. The control signal program plugs also
loop certain input control signals back through the channel interface as output control signals
from the channel. For example, in some interface types Request to Send is an input to the channel;
the program plug may send the signal back through the channel interface as output control signal
Clear to Send. The result is that, when the channel device turns On Request to Send to initiate a
data transfer, Clear to Send also turns On immediately, because the state of Request to Send is
looped back to the channel device as control signal Clear to Send.
036R660-000, Issue 10
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CPU to Terminal - (CTA1)
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CPU to Terminal - DCD/DSR On (CTRL)
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CPU to Terminal -DSR On 1(',T(',11
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CPU to Private Line Modem (CPL1)
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CPU to Terminal-Polling (CPL2)
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CPU to Modem-Polling (CPM2)
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CPU to Dial-Up Modem (CDM3)
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Dial-Up Modem to CPU (DMC3)
System Overview
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