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Chapter 5. Communications Reference Data
5.1 Communications Facilities
5.1.1 3274 Models SIC and 52C SDLC
The 3274 Models 51C and 52C can communicate with the
following using synchronous data link control (SDLC):
• S/370 over full or half-duplex communications
facilities via a 3704 or 3705 Communications
Controller. See Figure 5-1, Part 1.
• 8100 Information System through a directly attached
loop or through a data-link attached loop. See
Figure 5-1, Part 2.
5.1.2 3274 Mode/51C BSC
The Model 51 C communicates with an S/370 or
S/360 using binary synchronous communications (BSC)
over duplex or half-duplex communications facilities
via a 2701 Data Adapter Unit, a 2703 Transmission Control
Unit, or a 3704 or 3705 Communications Controller. See
Figure 5-1, Part 1.
The Model 51C can communicate with the following
using BSC:
• S/370 Models 115,125,135, or 138 via the appropriate
BSC features on the 3115, 3125, 3135, or 3138. See
Figure 5-1, Part 1.
• The 4331 through its communication adapter.
5.1.3 3274 Models SIC and 52C Modes/Speeds
The 3274 Models 51C and 52C operate in half-duplex/
point-to-point mode or half-duplex/multipoint mode on
either half-duplex or duplex facilities. Transmission speeds
are 1200, 2000, 2400, 4800, 7200, and 9600 bps on
nonswitched facilities.
For loop attachment, Models 51 C and 52C operate in
half-duplex mode at the following speeds:
•
Direct attached loop - 9600 or 38,400 bps
• Data-link attached loop - 2400, 4800, or 9600 bps.
5.1.4 ConllnUllicatioll Adapters
5.1.4.1 Communication Common Adapter
The Communication Common Adapter (CCA) is used with
a transmission facility of SNA/SDLC or BSC. Clocking must
be provided by the modem or the Communication Facility
unless the CCA with clocking is installed in the 3274. When
the 3274 contains clocking, the line speed is set by the Line
Speed switch, located on the operator panel, and can be
either 1200 bps or 600 bps. The CCA with clocking is
required when a 1200-bps Integrated Modem is installed.
5.1.4.2 High-Performance Communication Adapter
The High-Performance Communication Adapter (HPCA) is
used with a transmission facility of SNA/SDLC. HPCA is
required when a line speed is used that is greater than
9600 bps (X.21 nonswitched at 48K bps, or DDS adapter
at 56K bps), when either the X.21 switched adapter or the
loop adapter is installed.
5.2 C01nmunications Attachnlents
5.2.1 External Modelll - EIA/V.35
An external modem, or equivalent device, with its own
clocking can be attached to a 3274 Model 51 Cor 52C
(w/o V.35). The 3274 must have the external modem
interface (EIA or V.35) and either a CCA or an HPCA
installed. The V.35 interface provides su pport for com-
munication line speeds up to 57 .6K bps for SDLC and
9600 bps for BSC on Model 51 C. The V.35 Interface Com-
munications Line Flow - Model 51 C is shown in Figure 5 -2,
a foldout at the back of this manual (page FO-l). Switched
network backup is available with auto answer/manual call
on IBM (EIA) modems. A determination should be made as
to the wrap capabilities of the modem being used. The 3274
communication line flow for EIA is shown in Figure 5-3.
5.2.2 Integrated Modenl ( 1200-bps)
The 1200-bps Integrated Modem feature provides for the
connection of the 3274 Model 51C to switched and
nonswitched telephone lines, and the connection of the
3274 Model 52C to nonswitched telephone lines. The
1200-bps Integrated Modem is compatible with the IBM
Mini-12 and 3976-3 modems.
Note: The operating speed oftlze IBM 3976-3 is only
1200 bps.
Chapter 5. Communications Reference Data
5-1
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