Texas Instruments 990 - Page 37

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DATA
CONTACT
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KEYS
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MATRIX
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26
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MODE
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FEEDBACK
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CIRCUIT
(A)136265
Figure 1-17. Model 911 VDT Keyboard Block Diagram
KEYSWITCH MATRIX
OT
THE Y SCAN LINES ARE IN
A PLANE PARALLEL, BUT N
IN CONTACT WITH, THE X
SCAN LINE PLANE. A TYPIC
KEYSWITCH HAS A DIODE IN
SERIES WITH IT AND THESE
TWO COMPONENTS RUN BE-
TWEEN A Y SCAN LINE AN
AL
D
AN X SCAN LINE.
(A)t 36266
XO
X1
X2
X3
X4
X5
X6
X7
X8
YO Y1 Y2 Y3 Y4
hl
L
I
I
7
l¥7
a
l
~
KBDT1
'
7
KBDT2
_,
7
KBDT3
~
7
KBDT4
~
7
KBDT5
'
7
KBDT6
'
7
KBDT7
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7
KBDTB
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7
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7
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7
TO
u2-s
Y5 Y6
I L
Jt-1
Jt-5
J1-6
J1-a
Jt-9
Y7
TO POWER/
LOGIC PWB
YB
Y9
L·L
Figure 1-18. Model 911 VDT Keyboard Contact Matrix
1-27
Digital Systems Division