IBM 3741 Data Station Reference Manual page 136

Chapter 14. I/O Adapter
The 3741 I/O adapter provides a high-speed method of en-
tering diskette data directly into a system or of building
diskette storage files directly from a system.
The I/O adapter and the data recorder attachment feature
are mutually excl usive.
The I/O adapter transfers data by either reading or writing.
Reading transfers data from the system to the 3741; writ-
ing transfers data from the 3741 to the system. Reading
and writing, as defined in the reference manual of the sys-
tem in communication with the 3741, may be exactly op-
posite due to the direction from which data is entering or
exiting the particular device.
When the I/O
adapt~r
is reading, the data is transferred at
an approximate rate of 1000 records per minute. When
writing, the data is transferred at an approximate rate of
1500 records per minute. These data rates are the capa-
bility of the 3741 I/O adapter, but not necessarily the
actual data rates when connected to a system; the determin-
ing factor is the data transfer rate of the system. See the
reference manual for the system for the actual data transfer
rate of each mode of operation.
The basic functions of the data station do not change with
the installation of the I/O adapter. During data transfer
operations, while the 3741 is actually communicating with
the system, the keyboard is disabled except for the N UM
SHIFT, ALPHA SHIFT, and RESET keys. These keys re-
main enabled to allow terminating an operation, although
terminating an operation by using these keys is not recom-
mended as a normal procedure because data may be lost in
the process. The normal termination procedure associated
with most of the operations allows for completion of the
data transfer before the operation is terminated. After the
3741 is done communicating with the system, the keyboard
will again be enabled before termination of the operation.
When the I/O adapter is not transferring data and the key-
board is enabled, the 3741 can be used for basic data entry
jobs.
Operations are terminated in three ways:
1.
130
Manual - At a point in the transfer operation when
operator action is expected and the keyboard is en-
abled, the operator can press FUNCT SEL upper and
2.
3.
T to end the operation. If the 3741 is not in a wait
state at that time, the operator must first enter the
device address of the system in position 1 before
pressing these keys. Manual termination should not
be used when reading.
Automatic - At the end of some operations, the data
transfer terminates automatically.
Immediate - At any time, in an emergency situation,
the operator can terminate an operation by pressing
both NUM SHIFT and ALPHA SHIFT while pressing
RESET. However, some
reco~ds
may not complete
the transfer from buffer to diskette.
You can transfer data beginning with any sector of a track
and ending with any sector of a track (deleted records are
ignored). The data transferred is referred to as a file of
data. A file can consist of multiple data sets residing on one
or more diskettes. Records in a data set may be any length
from 1 to 128 characters, but the record length cannot vary
within a file.
Since multiple data sets can reside on a diskette, you must
ensure that the extents of the data sets do not overlap. The
I/O adapter checks for overlapping extents, but does not
check for deleted or bypassed data sets. Sectors which are
deleted or which contain a sequential bad spot will also be
bypassed.
Dual disk capability provided on the 3741 is useful with the
installation of the I/O adapter feature when doing a file
transfer. Dual disk enables you to concatenate data on one
file from two diskettes when writing and also increases the
amount of data that can be transferred without operation
intervention.
FI LE TRANSFER
Data transfer by file is based on the extents in the data set
label and the selected mode of operation. The I/O adapter
checks the data set label for the following:
• Positions 1 through 3 must contain HDR
• Position 41 must not contain a B for bypass
• Positions 29 through 39 do not overlap the extents of
the other data sets on this same diskette