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Communications
Interface
Controls and Indicators
Options
Buffer Options
70/720 Asynchronous
Data Set Buffer
• The buffer operates with a communications interface
(to
data sets,
automatic calling units, etc.) which conforms
to
EIA Standard RS-232-B
(interface between data processing terminal equipment and data communi-
cation equipment).
The buffer can be operated without data sets when provision for such
operation is made in the appropriate remote device or system.
• The operator controls and indicators for the buffer are located on the
CCM Control Panel. They consist of the following:
Data (amber indicator) -
With a TC present, this indicator lights ex-
ceptwhen a spacing bit is transmitted. With an RC present, after the first
mark-to-space transition, this indicator lights except when a spacing bit
is received.
Select (patch panel) -
The buffer is easily connected to any CeM
Select (SEL) line and is thereby enabled when power in ON. When the
buffer is enabled, it responds to each SEL with BOP.
•
The buffer options described below are field- installable via WIrIng
changes. The buffer is originally conditioned for half-duplex, two-wire
operation, without any of the options.
• Four-Wire Operation -
This option is employed to eliminate the data
set turnaround delay with certain communications services and data sets
as follows:
Service
AT&T
Data Set
Dialed Network (2-wire)
103A
Half and Full Duplex
103F
Half and Full Duplex
202D
The effect of the option is as follows:
The RS signal to the data set is strapped in the on condition. Thus,
whenever CTS is on, transmission can begin.
1.
This option applies only to the Model 70/720-21
2.
This option can only be used when there is sufficient receive-to-
transmit turnaround delay built into the devices at each end of the
communtcations channel to allow each to accomplish the turnaround
from transmit-to-receive.
4-20
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