Principles of Operation
2-7
The 16.8V DC output is protected against over-voltage and over-power; the 12V and 3.3V DC
outputs are protected against over-voltage, short-circuit and over-current; the 5V DC output is
protected against over-voltage and short-circuit.
2.2.3 Key&displays board
2.2.3.1 General
The key&displays board provides the user’s interface. The main board supplies the power for
the key&displays board. The LCD module, 7-segment digit display, LED indicators and keys
are integrated on this board.
Principle diagram
STN LCD
module
Key
matrix
Start-up signal
Start-up
circuit
LED
CPLD
LED&KEY
OFF/STANDBY
detection
Switch
VSB
3.3V
ADV
3.3V
disable
Figure 6 Operation principle of the key&displays board
2.2.3.2 Units
2.2.3.2.1 LCD module
This module has the function of adjusting the contrast and brightness in 10 levels,
Self-provided drive.
The FPGA controls the LCD. It transmits data signals and control signals to the LCD drive to
realize the display on the LCD.
The main board supplies the 3.3V power for the logic part of the LCD module, and the power
board supplies the 3.3V power for the backlight assembly.
This module displays menus, trend data and plethysmograms.
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General