Service manual

ViewSonic Corporation Confidential - Do Not Copy VA902-3_VA902b-3

• Two clock output ports

• Two external interrupts, INT1 is shared with Slave

IIC interrupt source

• Maximum 4 channels of 6-bit ADC

• Flash-ROM code protection selection

• Hardware ISP (In System Programming), no Boot

Code required

• Embedded Dual Ports DDCRAM (128-byte x 2)

• Green products like Pb-Free Packages or All Green Packages available

PIN CONFIGURATION & DESCRIPTION

A “CMOS output pin” means it can sink and drive at least 4mA current. It is not recommended

to use such pin as input function.

An “open drain pin” means it can sink at least 4mA current. It can be used as input or output

function and needs an external pull up resistor.

An “8051 standard pin” is a pseudo open drain pin. It can sink at least 4mA current when

output is at low level, and drives at least 4mA current for 160nS when output transits from low

to high, then keeps driving at 120 uA to maintain the pin at high level. It can be used as input

or output function. It needs an external pull up resistor when driving heavy load device.

There is an internal pull-up resistance on each CMOS PAD and an internal pull-down

resistance on each input

Low Power Reset (LVR) & Watchdog Timer

When the voltage level of power supply is below 2.4V (+/-0.4V) for a specific period of time,

the LVR generates a chip reset signal. After the power supply is above 2.4V (+/-0.4V)

INVERTER

In order to drive the CCFLs embedded in the panel module, there is a half bridge inverter to

convert by the controller.

The input 12V up to hundreds of AC voltage output.

The inverter is formed by symmetric in order to drive the separate lamp modules.

The input stage consists of a PWM controller, half bridge inverter, and switching MOSFET to

convert DC input into AC output.

The output stage consists of a tuning capacitor, coupling capacitor, transformer, push-pull

MOSFET pair to boost AC output up to hundreds of voltage.

And one resister is serial to lamp for output voltage feedback.

There are two signal to control the inverter which come from system.

Logic “high” level which send to I901 is turn on the inverter.

BRI signal control brightness by DC level which was integral from PWM signal.