The Keyboard And Its Functions; Cursor; Nulls Vs. Blanks - IBM 3708 Description

Table 4-8 (Page 2 of 2).
NNN
Codes in Session Status Field
NNN
-RSP sent
Code Explanation to the host
PC 454 A screen size specification error has occurred. 0821
PC 455 An L U profile error has occurred. 0821
PC 456
An L U type-l error has occurred.
0821
PC 457 BIND for cryptography was specified but is not 0821
supported by the
CC 518
The 3708 received a segment with improperly
8007
sequenced TH MPF bits.
The Keyboard and its Functions
Cursor
Nulls vs. Blanks
The keyboard attached to the terminal allows the user to change, edit, or create
character displays. As messages are being composed or modified by keyboard
operations, the changes are remembered by the 3708. When the user completes an
operation and presses the ENTER key sequence (or other attention type sequence)
the data is transmitted to the host.
A special symbol, called a cursor, is displayed on the display screen to show where
the next character entered from the keyboard is stored. Depending on the device,
the cursor may appear as an underscore, as a blinking underscore, or as a
rectangular or blinking rectangular symbol imposed over a character. The device
may allow the user to change the appearance of the cursor. See the device manual
for instructions. The 3708 does not control the cursor appearance.
Successful keyboard entry of a character causes the cursor to advance to the next
character location within the field. In some cases, the cursor advances to the
beginning of the next input field.
On the display image, positions in input fields that do not contain characters may
actually contain either a blank character or a null character. In most usages, blanks
exist between other characters, and nulls exist in unused characters at the end of a
field. This difference affects the user in the following ways:
• When the space bar or key on the keyboard is pressed, a blank character is
placed in the field.
• When the cursor movement functions are used, no character is placed in the
field, so that positions that were null remain null.
• When the Insert function is used, there must be null characters to the right of
the cursor location. (See the description of the Insert function in "Key
Sequences for 3270 Functions" on page 4-46.)
• When the Delete function is used, a null character is placed at the end of the
field for each character deleted.
The 3708 feature called Enhanced Null/Blank Processing can be used to eliminate
some of the confusion caused by the way nulls and blanks are used.
Chapter
4.
Protocol Conversion Mode
4-45