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COMMUNICATION
EQUIPMENT AND
FACILITIES
(Cont'd)
OPERA TlONAL
CHARACTERISTICS
Signals
Commands
Disconnect (DISC)
Transmit (TC)
Receive (RC)
Notes:
70/720 Asynchronous
Data Set Buffer
1.
Four-wire (or equivalent), half-duplex operation permitted for
fast-turnaround or reverse-channel signalling.
2. Automatic calling permitted via the AT&T 801A or 801C Automatic
Calling Unit.
3. Reverse-channel signalling permitted on two-wire circuits.
4. Additional termination equipment is provided as a part of the
service.
• The 70/720 series of buffers operate as described in the following
paragraphs depending upon the buffer model involved, the remote device
and interconnecting facilities involved, and the commands it receives from
the CCM.
• Control signals and data bits are exchanged between the buffer and CCM
in a prescribed sequence:
1.
CCM selects the buffer.
2. The buffer presents its status signals and data level.
3. CCM issues command signals or a data level.
4. CCM drops Select, allowing the buffer to change its status signals
and data level.
Signal and data levels are accepted by the buffer and CCM at strobe
time. The buffer drops the report levels after receipt of RAK from the
CCM.
•
The command signals from the CCM are decoded by the buffer into the
following commands:
Disconnect (DISC)
Transmit (TC)
*End Character (ECC)
Receive (RC)
Auto-Call (ACC)
Terminate (TERC)
•
The DISC command restores the buffer and the data set to their quiescent
conditions; such that a message network line is disconnected at the end of a
call.
• The TC command conditions the buffer, the data set, and the line for
data transmission.
• The RC command conditions the buffer, the data set, and the line for
data reception.
*Model 70/720-11, only.
4-16
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