GE TruSat - Microcontroller; Display Board

TruSat Technical Reference Manual
2–4
Microcontroller
The System board microcontroller is responsible for system monitoring, user
interface processing, speaker control, display control, alarm LED control, RS-232
communications, SPI bus control, enabling oximetry hardware, and real-time clock
control.
The microcontroller is supplied by a +3 VDC signal, V_ON, which is always on when
power is applied to the board. V_ON and VDD are created from the battery by a
regulator. VDD is switched ON/OFF by the microcontroller.
An internal power supply monitor in the microcontroller resets the hardware if a
brown-out condition is detected. A watchdog micro clears the display and causes a
continuous tone to sound if no activity is detected.
2.5 Display board
I
2
C bus
Display board
connector
BATT +
+4.2 VDC
Alarm LED
Yellow
Alarm LED
Red
Line power LED
Green
ON/OFF ALARM
LCD
System board
connector
LCD drivers
Voltage regulator
Backlight
LCD_EN
Figure 2-3. Display board block diagram
The Display board contains the liquid crystal display (LCD) on which information
sent by the System board appears: oxygen saturation, pulse rate, PI
r
,
plethysmographic pulse bar (pleth bar), alarm limit settings, and screen symbols for
changing monitor settings. It also displays indicators for the battery, alarm silence,
lock status,. and alarm messages. The backlight, power switch, alarm silence switch,
line power LED, and red/yellow alarm LED are located on the Display board.
The Display board connects directly to the System board through a 30-pin board-to-
board connector. A BATT+ supplies power to the 4.2 V display regulator, which
optimizes the LCD contrast. Two LCD drivers can drive up to 160 segments on the 4.2 V
LCD, which contains 80 segment pins and 2 backplane pins.
The backlight can be switched ON or OFF by the user. It consists of 54 sets of 2 amber
LEDs.
The green AC power LED monitors the DC line voltage from the external power supply.
A microcontroller monitors the ON/OFF and ALARM switches on the board and drives
the red/yellow alarm LED.
The Display board is shielded from the effects of EMC.