ViewSonic VX912 Service Manual page 27

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... RTD2523(U7)
The heart of the system board is RealTek RTD2523. The RTD2523 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 24.576 MHz crystal is recommended.
b) Analog to Digital Converter:
The RTD2523 chip has three ADC's (analog-to-digital converters), one for each color (red, green and
blue) .The analog RGB signals are connected to RTD2523 as described
Pin Name
Red +
Red -
Green +
Green -
Blue +
Blue -
c) OSD : The RTD2523 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 RTD2523 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.
Pin number
1
13
14
41
40
42
34
9
2
27
26
16
17
ViewSonic Corporation
Pin Number
37
38
34
35
30
31
Pin Name Pin Number Usage
P5.2 Key / Power on ,off
P3.4 NV_RAM (U4) SDA
P3.5 NV_RAM (U4) SCL
P5.4 Key_down
P5.5 Key_right
P5.3 Key_up
P5.6 Key_left
P6.3 Key_mute
P5.1 Key_select
P6.0 LED_red
P6.1 LED_green
P6.2 LCD panel power1 on / off control
P1.0 Backlight on / off control
24
below
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VX912