Texas Instruments 990 Installation And Operation Manual page 100

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945423-9701
A MODE key is also available on the keyboard and is intended to be used by terminal control pro-
grams to place the terminal in a specific operating mode. The way in which a specific keyboard
character set is selected is illustrated below:
SHIFT CONTROL
UPPERCASE LATIN ARABIC
CHARACTER SET
up
up up down
up Lowercase Latin
up up down
down
up Uppercase Latin
down
up
*
down
up Shifted Latin
up up * up
down Arabic
down
up *
up down Shifted Arabic
*
down * *
*
Control
*Don't care.
The keyboard character sets are illustrated in figures G-2 through G-S.
G.3 DISPLAY UNIT
The Model 911 terminal provides a 305-millimeter (l2-inch) diagonal, high resolution display. The
screen can display 24, SO-character lines of data: a total of 1920 characters per screen. Three types of
dot matrix are provided by the terminal: a 5x7 matrix that is used for Latin characters, a 7xS for
smaller Arabic characters, and a 7xlO dot matrix for the more intricate Arabic characters. All
characters fit into a single character position on the screen.
G.4 DEVICE SERVICE ROUTINE INTERFACES
In the Model 911 Arabic VDT, a special ROM is used that contains over 115 different character
shapes for the Arabic language alone. The shape displayed can be programmed to meet the re-
quirements of the Arabic language itself. In general, a character has a different shape depending on
its position in the word: isolated, beginning, final, or medial. The appropriate shape provided in the
display ROM is selected by the user's DSR according to the context in which a data character is
entered. To map the keyboard data entered to the displayed data and to the user buffer, a user DSR
has to handle three interfaces: the keyboard/DSR interface, user buffer DSR interface, and the
display/DSR interface. Figure G-9 is a simplified interface overview of the VDT controller. The
character tables used at each interface are designed to maximize the efficiency with which the inter-
face can be handled. These character sets are listed in figures G-lO, G-11, and G-12.
11
12 13
29 30 31
32 33
34
49 50 51
52
53 54
69
70 71
72 73
74
87 88
Figure G-2. Arabic Keyboard Key Numbering
G-2
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