Pioneer A-X700 Service Manual - Page 9
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7. CIRCUIT
DESCRIPTIONS
Function Switching
If one
of the
switches
S501
thru
S506
in
Fig. 7.6 is pressed, the PD6027
microcomputer
(IC401) detects which switch has been pressed, and
by
controlling
the
TC9162N
electronic
switch
(IC102), switches the unit to the selected function.
H
a pi
tt
Fig. 7-1
Key
scanning is started only when
one of the
keys in the matrix is pressed. PO thru P3 are all at
L level before any key is pressed, but are switched
to H level once a key is pressed. At the same time,
a microcomputer reads which key has been pressed
at KO thru K3, and then decides whether the pres-.
sed key is a function key or a volume
key. If a
function key, the current function position is com-
pared with the pressed function. If this comparison
shows that the two are different functions, func-
tion data corresponding to the pressed key is pas-
sed to the TC9162N.
The configuration
of this
data is outlined in Fig. 7.2.
Switch
scare
re ae a ew)
a
ce
Bit 8 is
ck
not used
'
2
3
4
5
6
7
8
9
10
"
12
13
14
=
st
The switch is activated at 'this rising edge
Fig. 7-2
cr | ce | cs
The data consists of 14 bits with bits 1 thru 7
corresponding to PHONO,
TUNER,
CD, etc., and
the bit for the switch to be switched on is switched
to H level. Bits 9 and
10 are the left and right
channel
selector bits, while
bits 11 thru
14 are
TC9162N code bits.
Volume Control
Volume
control
operations involve the use of a
microcomputer
(IC401)
combined
with
the
TC9177P
electronic
volume
control
(IC101)
as
indicated in Fig. 7.7.
Selector
2dB step
it
attenuator
1008 step
attenuator
Chip select bit
Loudness
ON/OFF
Fig. 7-3
20-Bit serial data corresponding to the pressed
key and the current volume level is passed from the
microcomputer for both left and right channels in
that order. TC9177P
(IC101) stores the 20 bits of
data in a 20-bit shift register, and then activates
each switch by strobe signal to achieve the selected
degree of attenuation.
If bit 3 of the data is switched to H level, LS-1 is
switched on and LS-2 is switched off resulting in
the loudness
being switched on to achieve a loud-
ness effect if the volume level is less than -20dB.
Muting
TC9177P
(IC101)
attenuation
is changed
by
20dB by data similar to the VR control data.
Volume UP & DOWN
Switches
"1
Volume indicator attenuation
Lighting
points
-~%
we
OO
Vow
Oo
aed
-70
-60
-50
-40
-30
-20
-10
Attenuation
° [dB]
Fig. 7-4
L and R Balance Switches
Pressing the L (S509) or R (S510) balance switch
once
results
in the display being switched
to a
balance display. Pressing either switch continuous-
ly results in continuous switching operation, and
pressing both together results in the balance being
set to center.
13
Attenuation
(dB)
Balance display attenuation
aan')
1210
8
6
42
0
2
46
B 10 12
14
Fig. 7-5
Lighting
points
0808
oOS07
5
os03
0$02
0804
D506
ixe
ike
ot
Forerion
J
=a
fee)
goer
| rome
°
E
°
$301
Display
unit
$501 | PHONO
$302 : TUNER
$503
co
$804
viDEO/auX
S505:
TAPE
S506. ADAPTOR /TAPE 2
$510; BAL RIGHT
SS(3° METER RANGE (150
-10W}
S301; w/s (W-8)
Level
shift
Level
shift
POWER AMP
$807: vou UP
$508: VOL DOWN
$512 | Muting switch
S511.
LOvONESS.
Fig. 7-7
Display
——» Output