ViewSonic VP150M Service Manual - Page 43

Service

Manual

VP150m

ViewSonic

September

2000

-

Version

1.0

THEORY

OF

CIRCUIT

OPERATION

HN

Present

Check

The

Hpresent

function

checks

the

input

HSYNC

pules,

Hpre

flag

is

set

when

HSYNC

IS

OVER

10KHz

or

cleared

when

HSYNC

is

under

10Hz.

The

Vpresent

function

checks

the

input

VSYNC

pules,

the

Vpre

flag

is

set

when

VSYNC

is

over

40Hz

or

cleared

when

VSYNC

is

under

10Hz.

A

control

bit

"PREFS"

selects

the

time

base

for

these

functions.

The

HPRchg

interrupt

is

set

when

the

Hpre

value

changes.

The

VPRchg

interrupt

is

set

when

the

Vpre/Cvpre

value

change.

However,

the

Cvpre

flag

interrupt

may

be

disabled

when

S/W

disable

the

composite

function.

Output

HBLANKNBLANK

Control

and

Polarity

Adjust

The

HBLANK

is

the

mix

output

of

HSYNC

and

self

-test

horizontal

pattern.

The

VBLank

is

the

mix

output

of

VSYNC,

CVSYNC

and

self

-test

vertical

pattern.

The

mix

selection

and

output

polarity

are

S/W

controllable.

The

VBLANK

output

is

cut

off

when

the

VSYNC

frequency

is

over

200Hz

or

133Hz

depends

on

8MHz/12MHz

OSC

selection.

The

HBLANK/VBLANK

shares

the

output

pin

with

P4.1/P4.0.

Page

42

Confidential

—

Do

Not

Copy

ViewSonic VP150M Service Manual - Page 43

ViewSonic VP150M - 15" LCD Monitor Manual

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