Ibm 2715 Transmission Control Unit; 2715 Tcu F U N C T Io N S - IBM 2790 Manual

The 2715 TCU is a core-storage, buffered, microcoded, con­
trol unit capable of providing the user with a system-
controller function to which 2790 Data Communication
System terminals are attached.
2715 T C U FU N C T IO N S
• Provides controls to read from and write on 2790
terminals.
• Sets 2791 Area Station guidance lights in accordance with
a user-supplied transaction list.
• Checks for valid data transmissions from 2790 terminals.
• Assembles single and multiple data entries from 2790
terminals in accordance with user predefined steps
located in the 2715 transaction-list table.
• Transmits transactions assembled from 2790 terminals to
System/360 via a Multiplexer Channel Adapter or a Binary
Synchronous Communications Adapter.
• Provides for transaction expansion, which is the ability to
enter up to 81 transaction types from either a 2791 Area
Station or a Data Entry Unit.
• Performs error checking and error recording.
• Adds time-of-day (in hours and minutes) to provide a
time stamp (24-hour clock only) for each transaction
from 2790 terminals.
• Broadcasts time of day (12-hour clock or 24-hour clock)
to all 2791 Area Stations.
• Receives messages from System/360 and routes them
either to 2790 output printer, or to an attached 2740
Model 1 printer.
• Stores transactions from 2790 terminals on integral disk
storage for subsequent retrieval and transmission to
System/360.
• Provides for data recovery from the disk in case of system
failure.
• Provides for Initial Control Program Load from integral
disk storage.
• Provides self-diagnostics and terminal diagnostics stored
on integral disk storage.
• Provides data service and control for an IBM 2740 Com­
munication Terminal Model 1 attachable to the 2715.
• Provides an audible alarm and contact closure. The con­
tact closure is a switch available for operating an external
customer-owned device.

IBM 2715 Transmission Control Unit

The basic 2715 TCU (Figure 17) contains 16K (16,384)
bytes of core storage and an integral disk storage unit having
a data capacity (work area) of 450K to 870K bytes, depend­
ing on the amount of disk sorting. User tables are assembled
at System/360 and transferred to the 2715 TCU via the data
link. The 2715 operates with these tables to provide control
and data service for attached 2790 terminals. Data assembled
from 2790 terminals may be routed on a priority basis to
System/360 when the 2715 is operating in the on-line mode,
or it may be temporarily stored on the 2715 TCU integral
disk and subsequently transferred to System/360 on a sched­
uled basis. The user tables assembled by System/360 for the
2715 must contain a routing designation for each type of
transaction. This routing designation is defined by the user
when preparing transaction-iist statements for each type of
transaction used at area stations and data entry units.
A route designation of "disk" (deferred data) instructs
the 2715 to place this type of a completed transaction on
its integral disk storage device. Transactions are stored into
blocks of 640 bytes of core storage and are then transferred
to the disk. When the 2715 is in deferred-data mode and
no priority data is queued for transmission to the processor,
blocks of deferred data are transferred from the disk to
the System/360 processor. If the 2715 is not in deferred-
data mode, no attempt is made to transfer deferred data to
the processor under normal operations. Approximately
600,000 bytes of disk storage are available for user data.
The 2715 does not reuse the disk storage area until
System/360 has accepted all the user data stored on the
2715 disk, and a "reinitialize disk" request has been made
and honored.
A route designation of "CPU" (priority data) will in­
struct the 2715 to transmit this type of completed trans­
action to System/360 on a priority basis. The 2715 will
queue completed transactions of this type (in core storage)
for transfer to System/360 via the data link. If System/360
is not providing adequate data service for priority data, the
2715 will store this data on its disk. When adequate data
service is resumed, the 2715 will automatically fetch any
priority data on disk and transfer it to System/360. Com­
pleted transactions in 2715 core storage with a routing
designation of "CPU" may precede and be interspersed
with priority data stored on disk. Thus, sequence of priority
data cannot be assured if the System/360 does not continu­
ously provide adequate data service.
Direct attachment to System/360— either via the 2715
Model 1 Multiplexer Channel adapter, or the 2715 Model 2
IBM 2715 Transmission Control Unit 25