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Display Fields
foII4~--------
80 Character Positions
---------~~I
- - r - -
o
80
160
240
320
400
480
560
640
720
800
24 Rows
880
960
1040
1120
1200
1280
1360
1440
1520
1600
1680
1760
1840
1920-Character Display Format
Figure 4-3. Buffer Addressing Layout for 1920-Character Tenninal
79
159
239
319
399
479
559
639
719
799
879
959
1039
1119
1199
1279
1359
1439
1519
1599
1679
1759
1839
1919
A formatted display contains display fields defined by the host program. These
fields consist of blocks of character positions bounded by control characters. The
control character at the start of a field is set by the host program to determine the
characteristics of the field. This character contains the field attributes. Fields
containing character positions on more than one row "wrap" from the last character
position on one row to the first character position on the next row. A field may
wrap the screen. If the first character position on the screen does not contain a
control character, the last field on the screen wraps from the last character position
to the first. (Some field oriented operations are terminated early if the field wraps
the screen. This effect is noted in the descriptions of the specific operations.)
Display fields simplify operations both for the operator and for the programmer.
Headings can be displayed to prompt the operator as to the data that should be
entered; and the program can identify fields that contain entered data without
reading the entire display buffer. When data is being entered into a formatted
display, the presence of a control character acts as a tab stop. Pressing the tab key
advances the cursor from its current position to first character position in the next
unprotected field. (An
unprotected field
is one that accepts data input from the
keyboard.)
To define the start of a field, the program may issue a Write command transferring a
Set Buffer Address (SBA) order and a Start Field (SF) order to the 3708. The
specified buffer address is selected, and the control character specified by the SF
order is loaded into the addressed location. Only the start of a field is defined.
Starting a new field ends the previous field at the character position prior to the new
control characters.
4-30
IBM 3708 Description
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