NEC MultiSync LCD1550V Service Manual page 73

2.3 PIO (General-purpose port) (Circuit diagram: MAIN Board P.3/5)
2.3.1 Key scan status
U3 GPIO20 (pin 203) Key2-1 and GPIO 17 (pin 80) Key1-2 output pulses continuously. If Keys are pressed,
microcomputer will detect U3 signal to judge which key is pressed.
2.3.2 D-sub cable status signal
U3 GPIO5 (PIN96) CABLE-DETECT
This is an IN/OUT supervisory signal for the D-sub cable.
It is set at the low level when the cable is connected.
2.3.3 LED control
U3 GPIO3 (PIN41) LEDY
U3 GPIO19 (PIN78) LEDG
These signals are used for the LED lighting control.
When GPIO3 is high the LEDY lit and GPIO19 is low the LEDG lit.
3. Input Image Enlargement Display Circuit
3.1 S9050 (Circuit diagram: MAIN Board P.1/5)
The S9050 (U3) is controlled through the internal microcomputer.
The S9050 is provided with the analog interface D-SUB (CN1) and the digital interface.
4. EEPROM Control Circuit
4.1 Data memory (Circuit diagram: MAIN Board P.3/5)
The display control data are held by the EEPROM (U9). These display control data are accessed through
the IIC bus of the microcomputer.
5. Auto-adjuster circuit control
5.1 Video level adjusting function
Functions of VIDEO RAM are also used for the automatic contrast adjustment (video level adjustment).
For the microcomputer, a maximum value of the entered one screen or the level data in the specified area
can be used.
This readout value is used for the black level setting and white level setting (contrast setting) for the VIDEO
amplifier.
7-3