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ViewSonic VG181 - Memory Device

ViewSonic VG181
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Service
Manual
ViewSonic
VG181
July
2000
-
Version
1.0
THEORY
OF
CIRCUIT
OPERATION
Memory
Device
The
flash
memory
(U13)
stores
the
program
code
of
the
firmware.
The
address
bus
and
data
bus
are
connected
directly
to
the
PW364
(U15)
which
includes
a
scaling
chip
embedded
with
a
186
CPU,
OSD
generator,
Sync
decoder,
and
frame
buffer.
The
MBM29LV400
(U13)
is
a
4M
bits,
3.0V-only
flash
memory
organized
as
512K
bytes
of
8
bits
each
word
or
256K
bytes
of
16
bits
each
word.
The
devices
are
designed
to
be
programmed
in-system
with
the
standard
system
3.0V
Vcc
supply.
12.0V
Vpp
and5.oV
Vcc
are
not
required
for
write
or
erase
operations.
The
devices
can
also
be
reprogrammed
in
standard
EPROM
programmers.
In
order
to
eliminate
bus
contention
the
devices
have
separate
chip
enable
(/CE),
write
enable
(WE),
and
output
enable
(/OE)
controls.
The
MBM29LV400
are
pin
and
command
set
compatible
with
JEDEC
standard
EEPROMs.
Commands
are
written
to
the
command
register
using
standard
microprocessor
write
timings.
Register
contents
serve
as
input
to
a
state-machine
which
controls
the
erase
and
programming
circuitry.
Write
cycle
also
internally
latch
address
and
data
needed
for
the
programming
and
erase
operations.
Reading
data
out
of
the
devices
is
similar
to
reading
from
5.0V
and
12.0V
flash
or
EPROM
devices.
The
devices
feature
single
3.0V
power
supply
operation
for
both
read
and
write
functions.
Internally
generated
and
regulated
voltages
are
provided
for
the
program
and
erase
operations.
A
low
Vcc
detector
automatically
inhibits
write
operations
on
the
loss
of
power.
The
24LC16
(U14)
is
a
general
16K
bits
Electrically
Erasable
PROM.
It
allows
the
VG181
to
save
most
parameters
of
the
OSD
functions,
such
as,
contrast,
brightness,
H/V
position,
H-size,
phase,
etc.
Some
of
these
values
are
global,
but
some
are
independent
by
each
input
timing.
The
device
is
organized
as
eight
blocks
of
256
x
8
bit
memory
with
a
2-wire
serial
interface.
Low
voltage
design
permits
operation
down
to
2.5
volts
with
standby
and
active
currents
of
only
5uA
and
1mA
respectively.
The
24LC16
has
a
page-write
capability
for
up
to16K
bytes
of
data.
Page
26
Confidential
-
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