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4. Internal/External
source selection
This circuit is for the selection of external AV input source or internal source. The external AV
source (AV1 and AV2) are applied to the AV switching
IC, IC801. When the AV1 mode is
selected, the AV1/AV2 switching signal from pin 9 of the CPU outputs "Low" to pins 9, 10 and
11 to select the AV1 source, and then the video, audio-L and audio-R signals are sent from
pins
4, 15 and 14 to the next stage
respectively.
In
the video signal, the selected external video signal is supplied to pin 15 of IC101 and the
internal video signal supplied to pin 13. The selection of internal or external video source is
performed in the IC101 by the TV/AV drive signal sending from pin 10 of the CPU via inverter
transistor Q202.
In the audio signal, the selected
audio signals(L/R)
are supplied
to the sound control
IC,
IC1l 02, MC44131 PB, and the selection of external or internal audio source is performed
by
the bus lines.
The following tables show the TV/AV and AV1/AV2 switching logic output from the CPU.
Iclol
–13
k
)
–15
-..16
J
I ternal Video Input
;xternal Video Inpu
Q202
0 ~;;
VIDEO
IN
O AV1 AUDIO L.IN
0 AV2
~~~
'uD'OR-'N
IC801
\
AVIIAV2 switch
4'"
Internal Audio L/R
1
16
External
Audio
15
L
g
*
5
3
...........
14
R
bm
H
K&
4
SG
mm;
o=
~3~
@
{:
11
;;
.......
~:
A
;:
~;
10
/ ; Bus
. ...................
9
AV1 IAV2
12113
..........................
9
SCIJ
TVIAV
SDA
10
CPU
4
SPEAKERS
AA1-A
-25-
AA1-A
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