29
ViewSonic Corporation
Confidential - Do Not Copy
VX2255wmh-4
VX2255wmb-4
4. Circuit Description
4.1 MAIN BOARD
The main board is a two-layer, single-landed design with ground and ground planes provided.
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 3 functional areas: flat panel controller, Micro controller and audio controller.
4.1.1 Flat panel controller…NT68625F (U3)
The heart of the system board is NovaTek
NT68625F. The NT68625F is a graphics processing IC for
LCD monitor. It provides all key IC control functions required for LCD panel. On-chip functions
include a high-speed triple-ADC, TMDS receiver, PLL, high scaling engine Micro processor and
OSD controller, manages other devices in the system such as the keypad, the backlight, LED and
audio general purpose input/output pins.
a) Clock Generation:
Crystal Input Clock (OSCI and OSCO). This is the input pair to an internal crystal oscillator and
Corresponding logic. A 12MHz crystal is recommended.
b) Hardware Reset (Pin 48)
Hardware Reset signal is generated by NT68625F (U3/Pin 48). It assert a reset signal at least
1ms.
c) Analog to Digital Converter
The NT68625F chip has three ADC's (analog-to-digital converters), one for each color (red, green and blue).
The analog RGB signals are connected to NT68625F as described below
Pin Name
Pin Number
R+ 24
R- 25
G+ 22
G- 23
B+ 19
B- 20
Pin number
Pin name
Pin function
39 PA6 Key-Menu
125 AD1
Key-Sel/Auto
124 PC5
Key-Power
on/off
125 PB0
Key-Right
126 PB0
Key-Left
66 PA0 LED-amber
65 PA2 LED-green
28 PA3
40 PA7
118 PWMB Backlight-adj.
49 DDCD_SDA
SDA-VGA
(Debug)
50 DDCD_SCL
SCL-VGA
(Debug)
31 DDCA_SDA/RS232_TX
SDA
(Debug)
32 DDCA_SCL/RS232_RX
SDA
(Debug)
Содержание VX2255wmb-4
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