ViewSonic VP150M Service Manual - Page 37

ViewSonic VP150M - 15" LCD Monitor Manual

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Service Manual VP150m THEORY OF CIRCUIT OPERATION ViewSonic September 2000 - Version 1.0 The PWM signal from AM101-1 is a periodical signal with a period that is 1023 times the period of the free-running clock connected to the pin "CLK_1M". System manufacturers may select any frequency for the free running clock. The default clock frequency is 1MHz. System manufacturers also decide the unit delay for the external delay circuit. The delay information is stored in the EEPROM. When the AM101-1 wants to delay the synchronization pulse for N units of delay, it will output the PWM with the high time equal to (N * the period of the free-running clock), and with low time equal to (1023-N)* the period of the free-running clock. When N=1023, the PWM signal stays high all the time, and when N=0, the PWM signal is always low. Free Running Clock As described in previous section, a free-running clock is needed for the AM101-1. This clock is used for many of the AM101-1's internal operations. PWM operation is one of them. System manufacturers can select the frequency of the free-running clock, and the default clock frequency is 1MHz. System manufacturers can use an oscillator to generate the free-running clock, and feed that clock directly to the pin "CLK_1M", or use a crystal connecting to "CLK_1M" and "CLK_11VI_O". Image scaling The AM101-1 supports several different input modes, and the input image may have different sizes. It is essential to support automatic image scaling so that the input image is always displayed to the full screen regardless the input mode. The AM101-1 scales the images in both horizontal and vertical directions. It calculates the correct scaling ratio for both directions based upon the LCD panel resolution and the input mode and timing information produced by the "Input mode detection & auto calibration" block. The scaling ratio is re-adjusted whenever a different input mode is detected. The ratio is then fed to the buffer memory read control logic to fetch the image data with the right sequence and timing. Some of the image data may be read more than once to achieve the scaling effect. Page 36 Confidential - Do Not Copy

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Service
Manual
VP150m
ViewSonic
September
2000
-
Version
1.0
THEORY
OF
CIRCUIT
OPERATION
The
PWM
signal
from
AM101-1
is
a
periodical
signal
with
a
period
that
is
1023
times
the
period
of
the
free
-running
clock
connected
to
the
pin
"CLK_1M".
System
manufacturers
may
select
any
frequency
for
the
free
running
clock.
The
default
clock
frequency
is
1MHz.
System
manufacturers
also
decide
the
unit
delay
for
the
external
delay
circuit.
The
delay
information
is
stored
in
the
EEPROM.
When
the
AM101-1
wants
to
delay
the
synchronization
pulse
for
N
units
of
delay,
it
will
output
the
PWM
with
the
high
time
equal
to
(N
*
the
period
of
the
free
-running
clock),
and
with
low
time
equal
to
(1023-N)*
the
period
of
the
free
-running
clock.
When
N=1023,
the
PWM
signal
stays
high
all
the
time,
and
when
N=0,
the
PWM
signal
is
always
low.
Free
Running
Clock
As
described
in
previous
section,
a
free
-running
clock
is
needed
for
the
AM101-1.
This
clock
is
used
for
many
of
the
AM101-1's
internal
operations.
PWM
operation
is
one
of
them.
System
manufacturers
can
select
the
frequency
of
the
free
-running
clock,
and
the
default
clock
frequency
is
1MHz.
System
manufacturers
can
use
an
oscillator
to
generate
the
free
-running
clock,
and
feed
that
clock
directly
to
the
pin
"CLK_1M",
or
use
a
crystal
connecting
to
"CLK_1M"
and
"CLK_11VI_O".
Image
scaling
The
AM101-1
supports
several
different
input
modes,
and
the
input
image
may
have
different
sizes.
It
is
essential
to
support
automatic
image
scaling
so
that
the
input
image
is
always
displayed
to
the
full
screen
regardless
the
input
mode.
The
AM101-1
scales
the
images
in
both
horizontal
and
vertical
directions.
It
calculates
the
correct
scaling
ratio
for
both
directions
based
upon
the
LCD
panel
resolution
and
the
input
mode
and
timing
information
produced
by
the
"Input
mode
detection
&
auto
calibration"
block.
The
scaling
ratio
is
re
-adjusted
whenever
a
different
input
mode
is
detected.
The
ratio
is
then
fed
to
the
buffer
memory
read
control
logic
to
fetch
the
image
data
with
the
right
sequence
and
timing.
Some
of
the
image
data
may
be
read
more
than
once
to
achieve
the
scaling
effect.
Page
36
Confidential
—
Do
Not
Copy