Omron 8025G Maintenance Manual page 110

THEORY OF OPERATION
SECTIOr--
omitted.
r - - - - - - - - -
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KEYBOARD CARD ---,
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SHIFT
AND
CONTROL
X-V
MATRIX
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Y.
'NW
TRAIN
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..
ENCODER
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L _________ ..J
~----I
LEDLATCH
~
-SVdc
~
LIGHT
EMITTING
DIODES
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B . . . . . . .---
POWER , ..... - - - -
ON/OFF
KDBO-8
CP
Ol
RPT
SPKR
115 V ae:
SWITCH t - - - -.. _
115V""
----.I
Figure 4-21. Keyboard block diagram.
In the 12 line display terminal, X-V matrix switches 58 through 69 are
Table 4-8 defines the active keys and their functions.
NOTE:
Unused keys are still active, but are inhibited by
software.
A series'of pulses, generated by the encoder chip, is sequentially ap-
plied to the X lines, and the Y inputs to the encoder arp serially gated. Thus,
each line c-an be detected individually. When a key is depressed (switch closure),
an X driver in the encoder is connected to a Y decoder, and the corresponding X-V
coordinates are determined.
The X-V coordinates are decoded in the encoder and converted to an ASCII
8-bit code by a ROM in the encoder. Each X-V coordinate can be converted into four
different codes throu~h the use of the shift and control keys. Mode lo~ic within
the encoder serves as an interface between these keys and the ROM.
Shift and lock (switches 2 or 13 and 15, respectively) perform the same
ftmction as the shift and lock keys on a typewriter, (i.e., shift from lower-case
to upper-case characters). The ASCII control code is generated when the control
key (switch 29) is depressed. Depressing both shift and control keys generates
additional codes.
After the ASCII code is generated, the charac~ is stored on KDB~-8 via
an output buffer in the encoder and the encoder sends a DSO signal (pin 9 of J7l
goes low) to the keyboard interface on the cursor control card. When data on KDB~­
is transferred to the A Data Bus
~
the keyboard interface, it sends an
or
signal
to the encoder via J71, pin 13. OE resets the strobe circuitry and enables the
output buffer circuitry for the next key stroke.
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