ViewSonic VG181 - Theory of Circuit Operation

Service
Manual
ViewSonic
VG181
July
2000
-
Version
1.0
THEORY OF CIRCUIT OPERATION
The operation of keypad
The
OSD
is
controlled
through
five
pins
and
an
LED.
As
shown
on
the
previous
page,
they
are
Power,
Auto,
+,
Function,
and
—
keys,
and LED.
1.
The
power
key
through
POW1
and
POW2
is
used
to
control
ck
of
CD4013.
A
pulse
is
sent
to
control power
while
pressing
the
power
key.
2. After power on, the other four keys are in the high state due to the pull up
resistor. They will transition to a low state dependent on which key is
pressed. The state will be determined by the PW364 through PORTCO to
PORTCS to activate the corresponding function.
3.
The
LED
is
bi-colored
with
green
and
orange
selections.
The
PW364
controls
the
LED’s through
PORTC4
and
PORTCS.
During
normal
operation
the
POCTCS5
(LED2)
is
set to a
high state
and
PORTC4
(LED1)
is
set
to a
low
state. These
will
reverse
during
power
saving.
Operation of the clock
1CS501
is
used
to
generate
the
memory
system
clock
(MCKEXT)
and
display
clock (DCKEXT). The power of ICS501 is filtered through L10, L31 and L32.
1. During normal operation the PW364 sets PORTA7 (CLKEN) to a high state
and enables CLK to output 100MHz.
2. While in the power saving mode, the PW364 sets PORTA7 (CLKEN) to a
low state and disables the CLK output. In this mode the LED is orange and
the screen is blank.
Page 10
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