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displays on
the DSP board
.
Lamps in the transport control
switches are also part of the
display
matrix
array
via
FET
control switches
on the
KBD
board
.
A 74 HC 138
(
3 to 8 line
decoder
)
is utilized in the display matrix
array
.
Using
this
configuration
,
a more expansive array can be realized
.
The keyboard matrix
array
consists of the top panel keys
and
switches on the
APR
-
5000
.
74 HC 138
3
to
8 line
decoder
.
Multiplexing is performed using a
4.5
.
15.2
Latched Address
Decoding
Various control signals and address lines are routed to the
KBD
board
,
bus
transeiver IC 1
.
receive
signals
from the CPU board
,
normally HIGH
(
+ 5
V
)
unless enabled
,
chip select signals
used for
enabling
the various
portions
of
the
KBD board
.
These are buffered
using a
74 HC 245
bi
-
directional
IC 1 is
configured
such that
it
will
only
The
outputs of
IC 1 are
These are the
active LOW
4.5
.
15.3
End
-
Of
-
Tape
(
EOT ) Sensor Circuit
The EOT sensor
circuitry
is also
found
on the
KBD board
.
This consists of the adjustable
op
-
amp comparator
circuits
(
for sensor
)
and the
LED
driver circuit
( Q
9
)
.
The
comparators are fed from
the
photo
-
transistor in the EOT
assembly via pin 3
of CNJ
-
443
.
Adjustment
of the EOT
sensitivity is
performed by
the
potentiometers
RV
3
&
RV 4
.
Two
circuits are included so that each may be set to a
different
sensitivity
(
for instance
,
one for
sensing
leader
tape and
the other for
sensing
the
presence
of
recording
tape
)
.
Most
applications require
the use of
RV 4
as the
adjustment
.
The
output
of this circuit is returned to the
8279 via
RL
1
( Return
Line 1
)
.
The 8279 encodes the data for
output
to the CPU
.
* *
NOTE
:
If the CPU does not receive
this data from the
KBD
,
all transport functions are
disabled
.
4.5
.
15.4
MVC Touch Sensor Circuit
The Manual Velocity Control
( MVC )
wheel on the
top panel of
the
APR
—
5000
is made of metal and is directly connected
(
via
the PC board trace
)
to
R
63
.
R
63 is the input resistor for
the MVC touch sensor circuit configuration of IC 22
(
2
/
2
)
and
IC 8
( LM
-
311
)
.
The
capacitance
of the human body w i l l be
sensed at the
input
of IC 22
,
this causes a toggle of the
4
-
48
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