Dynapro Technologies Dynapro ET TCS, Application Developer'S Manual

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5-2
Because each character set contains 128 characters, graphic codes with values less than 128
decimal (80 hexadecimal) display characters from within the Standard Character Set. Graphic
codes with values greater than or equal to 128 decimal (80 hexadecimal) display characters from
within the Extended Character Set. Refer to Figure 5-1.
Only those characters within the character sets that correspond to graphic codes can be directly
displayed. Characters within the character sets that are stored at locations corresponding to
control codes are only displayable indirectly (not by sending the corresponding code). This
restriction occurs because codes that correspond to these locations within the character sets are
defined by ANSI to be control codes that cause special actions. See the Control Codes heading in
Chapter 3 for a description of how and when such characters can be displayed.
Since code values below 128 decimal can be represented using only 7 data bits, whereas code
values of 128 decimal and above require 8 data bits, the Standard Character Set can be accessed
using only 7 data bits, but the Extended Character Set cannot. The Select Character Set
Command described later in this chapter must be used to gain access to the Extended Character
Set when communicating using only 7 data bits.
The characters within the Standard and Extended Character Sets can be changed by the host
program as described later in this chapter. The default contents of the Standard and Extended
Character Sets are shown in Appendix C.
7KH&XUVRU
Each screen within the TCS contains a cursor. The cursor is a visual marker that identifies the
location on the screen where the next character is to be displayed. Normally, the next graphic
code received by the TCS designates a corresponding character from either the Standard or
Extended Character Set that is displayed at the cursor location, and the cursor is advanced to the
next location.
The cursor plays a key role in the display of characters on a screen because it determines the
location where the next character will normally appear. The movement of the cursor during the
display of characters is controlled by two modes: the Auto Wrap Mode and the New Line Mode.
Both modes are described in detail under the heading Character Interpretation Commands further
on in this chapter. In addition, certain control codes, known as format effectors, are generally
sent by the host to control cursor movement while characters are being displayed.