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Chapter 3. Data Station Operating Information
The entering, updating, verifying or finding of data on a disk
is performed by the data stations using different modes of
operation. The sequence of operations performed by the
control unit within the data station is directly depende.nt
upon the mode in which the station is functioning. Buffers
store and transfer data within the station to allow
communication between the keyboard, disk, and display.
Each mode of operation is unique, and, therefore, the use of
buffers, keys, and the information displayed is different for
each mode.
The mode of operation is indicated by a code displayed on
the status line of the display unit. Some of the modes <?f
operation for the 3741 and 3742 and their corresponding
display codes are:
Mode
Display Code
Enter
E
Update
U
Verify
V
Field correct
C
Search
S
Read index
X
Modify
M
Field totals (offline)
F
BUFFERS
Buffers are used to communicate with the keyboard, display,
and disk. The buffers are the current record buffer, previous
record buffer, hold buffer, and several format buffers.
The current record buffer stores data characters as they are
keyed or receives records that are read from disk during
update mode. Data information displayed on the screen is
from the current buffer.
The previous record buffer normally contains the last
completed record. Data is written on the disk from this
buffer and can also be dupl icated and placed in the current
record buffer.
The hold buffer is used to store the next record to be
processed when verifying data or to store a mask used during
search operations.
MODES OF OPERATION
Enter Mode (E)
Enter is the most basic mode of operation. Enter mode
can be selected from the index track only; an M error
results if enter mode is selected when in any other position
on the disk. Enter mode is used to write new information
on the disk. To select the enter mode, press FUNCT SEL
lower and then press ENTER.
As the operator keys a record, the data is stored in the
current record buffer until the record is completed. When
a record advance occurs, the completed record is trans·
ferred to the previous record buffer. While the next
record is being keyed into the current record buffer, the
previous record is written on the disk.
The data flow is summarized in Figure 9. When enter
mode is selected, the disk is positioned at BOE; the
current record buffer and the previous record buffer are
set to blanks. The station is then ready to accept data
keyed into the current record buffer.
As data is keyed, it is
stored in the current
record buffer and
displayed on the
screen.
At record advance,
the data is moved to
the previous record
buffer and the current
record buffer is filled
with blanks. At the
same time that the
next data record is
being keyed, the
record in the previous
record buffer is
written on the disk.
~
Keyboard
0,--1 _ _
-'I
•
o
Disk ..... _ _ _ _ _
OJ
Page 10
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