IBM 2790, Manual

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Programming Considerations
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The 2715 is a buffered core storage, microcoded control
unit, providing the user with a flexible central controller to
which area stations, data entry units and other I/O devices
are attached. For purposes of this section, the user is
assumed to be controlling the system at the System/360
and the operator is operating and monitoring the system
at the area stations and data entry unit locations.
The 2790 provides the user with a flexible communication
and information system. To achieve this, the user provides
a set of statements describing the processing that his input
must undergo. Since the 2715 is a hardware and microcode
type controller, it does not allow for complete user coding
control. Instead, the microcode interprets control require­
ments by means of a set of user-specified tables. These
tables contain pointers and index values as well as parameters
for the microcode.
The programming data link between the System/360
and the 2715 is through the binary synchronous communi­
cations (BSC), whether the attachment is local or remote.
Remote attachment line speed permits a maximum data
rate of 600 characters per second; local attachment permits
approximately 3000 characters per second. The maximum-
size message that can be transmitted from the 2715 to
I System/360 is 614 bytes, excluding BSC framing control
characters. All messages are transmitted in EBCDIC trans­
parent code.
S Y S T E M O P ER A T IO N
Data transactions, which originate on one of the devices
attached to the 2715, are formatted into messages and
either transmitted to the integral disk unit in the 2715 for
later retrieval by the user’s BTAM program or are sent
directly to the System/360 without any intervening delays.
Messages from System/360 are sent to the 2715, which
acts on them immediately. These messages may be directed
to output devices attached to the 2715, or they may be
control-type messages that call upon the 2715 to modify
its operaton in some way. If either the 2715 or the Sys­
tem/360 is incapable of receiving data for a temporary
period, normal BSC control sequences indicate this, and
the sender must wait. Should the data link be disabled for
some reason, the 2715 will enqueue all messages received
for later transmittal.
Transactions may be blocked together to make one
longer message, or be sent singly. This function is performed
automatically by the 2715 microcode on 2715 to Sys­
tem/360 messages, and performed by the user’s problem
program on System/360 to 2715 messages.
OS and D OS Support
Telecommunications support under both OS/360 BTAM
and DOS/360 BTAM is being expanded to include support
for the 2715 Transmission Control Unit.
This support consists of modifications to BTAM and
new Assembler Macro definitions to support generation
of user table-defining statements to object format. For
detailed programming information, see Systems Reference
Library manuals,
IBM System/360 Operating System,
Basic Telecommunications Access Method, GC30-2004;
or IBM System /360 Disk Operating System, Basic Tele­
communications Access Method, GC30-5001.
BTAM Modifications
Two main modifications have been made to BTAM. One
provides for centralized logging of errors collected by the
2715 relating to devices attached to it. This facility is use­
ful for Customer Engineering maintenance of the 2715
complex. The second provides for 2715-originated messages
to be printed on the System/360 console. This means that
the System/360 operator can receive operator-awareness
type messages if the 2715 has no 2740 attached or if the
2740 requires intervention.
2715 User Table Assembly
Seven DOS/360 and OS/360 Assembler Language macros
define user tables for the 2715. The user tables define the
hardware configuration, the step-by-step terminal functions,
and the related 2715 functions.
CONFIGUR. The CONFIGUR macro is used to generate the
table definition block, which contains pointers to the 2715
tables.
AS. The AS macro is used to build an entry in the area
station table and the data entry unit tables, and a corres­
ponding entry in the data entry unit index table.
TGROUP. The TGROUP (transaction group) macro is used
to define entries in a TGROUP table. Each keyword operand
associates a transaction list with a transaction code. A maxi­
mum of 63 TGROUP macros are allowed.
TRLIST. The TRLIST (transaction list) macro is used
with the area station list (ASLIST) macro and the data
entry unit list (DEULIST) macro to define a transaction.
When the transaction is initiated by an area station, the
TRLIST macro is followed by one or more ASLIST macros.
When the transaction is initiated by a data entry unit, the
Programming Considerations 61