ViewSonic vx912-1 Service Manual page 26

6. THEORY OF OPERATION
This section describes the function of the LCD monitor per functional block.
This monitor includes MB board, power board and button board.
6.1 MB BOARD
The MB board is a two-layer, single-landed design with ground and internal planes provided. DC power from the
power board enter the board through a 6P connector. Other connector on the board is for button board .The VGA
cable is a signal cable that contains video signal, sync signal and DDC signal from PC VGA adapter. This system
board consists of 4 functional areas : flat panel controller, MCU with flash ROM , power regulator .
6.1.1 Flat panel controller... MST8131A (U3)
The heart of the system board is MStart MST8131A. The MST8131A is a graphics processing IC
for LCD monitor. It provides all key IC functions required for LCD panel. On-chip functions include a
high-speed triple-ADC , PLL, high scaling engine, OSD controller.
a) Clock Generation :
Crystal Input Clock (TCLK and XTAL). This is the input pair to an internal crystal oscillator
and corresponding logic. A 14.318 MHz crystal is recommended.
b) Analog to Digital Converter:
The MST8131A chip has three ADC's (analog-to-digital converters), one for each color (red,
green and blue) .The analog RGB signals are connected to MST8131A as described
c) OSD : The MST8131A has a fully programmable ,high-quality OSD controller. The on-chip static
RAM(4096 words by 24 bits) stores the cell map and the cell definitions.
d) MTV312 Micro controller: The MTV312 micro controller(MCU) serves as the system micro controller. It' s
programs the MST8131A and manages other devices in the system such as the keypad, the backlight, LED,
audio and non-volatile RAM. using general purpose input/output (GPIO) pins.
ViewSonic Corporation
Pin Name
Red +
Red -
Green +
Green -
Blue +
Blue -
Pin number Pin Name
21 P1.3
13 P3.4
14 P3.5
25 P1.7
9 P6.3
24 P1.6
16 P6.2
37 P4.1
34 P5.6
23 P1.5
42 P5.3
41 P5.4
32 P6.6
Pin Number
63
62
60
59
58
57
Pin Number Usage
Key / Power on ,off
NV_RAM (U4) SDA
NV_RAM (U4) SCL
Key_down
Key_right
Key_up
Key_left
Key_mute
VGA connector
Key_select
LED_red
LED_green
LCD panel power1 on / off control
23
below
Confidential - Do Not Copy
VX912