Display Unit Controls And Indicators; Data Indicators Sample Pattern - Texas Instruments 990 Installation And Operation Manual

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945423-9701
Keyboard interpretations for the four United States modes are shown in figures 3-6 through 3-9.
(Refer to the appendixes for the European and Japanese keyboard mode interpretations.) The
related input/output (I/O) software examines the code to determine the function. The repeat
feature permits the operator to hold down the REPEAT key and then press any other key to gen-
erate the accompanying character (or function) at a rate of 10 ± 2 characters per second.
4.3 DISPLAY UNIT CONTROLS AND INDICATORS
The display unit has controls and indicators in two positions on the display housing: the side
and rear of the cabinet. The following paragraphs describe the functions of each of these
controls and indicators.
4.3.1 CONTROL PANEL. Three controls mounted on the right side of the VDT monitor housing
comprise the control panel. Figure 4-2 shows the controls.
The ON/OFF switch is a rocker switch that controls ac power to the terminal.
The brightness and volume controls are rotary controls that allow the operator to vary the
brightness of characters on the display and the loudness of the audio alarm, respectively.
4.3.2 DATA INDICATORS. A row of 10 light-emitting diode (LED) indicators are located in
the center of the rear panel of the display unit housing as shown in figure 4-3. Figure 4-4 depicts
a closer view of the indicators.
When lighted, the rightmost indicator (S) indicates that the video sync pulse is being received
from the VDT controller. This indicator should always be lighted if computer interface cables are
properly installed, computer and VDT power is on, and the VDT controller is inserted into the
computer chassis and working properly.
When lighted the parity indicator (P) indicates that the parity bit sent to the VDT controller
with the last character bits was correct. This indicator should always be on if the system is
connected properly, power is on, and the display unit is transmitting data properly to the VDT
con troller.
The remaining indicators display the code of the character last entered on the keyboard. The
indicators light to display a one bit, and remain dark to display a zero bit. Figure 4-4 illustrates a
sample display for the character "A". The most significant bit (MSB) of the character code is on
the left; therefore, the indicators must be read from left to right.
CODE 0100 0001
2
41
16
CAPITAL A
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MOST SIGNIFICANT
DIGIT BIT
PATTERN 0001
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LEAST SIGNIFICANT
DIGIT BIT
PATTERN 100
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_ _ _ _
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DATA
TRANSMITTED
0 • 0 0 0 0
0
e e e
(A)134329
7
MSB
6 5
4 3 2
• LIGHTED INDICATOR (ON)
Figure 4-4. Data Indicators Sample Pattern
4-4
a
LSB
P
S
Digital Systems Division