GE Medical Systems Dash 3000, Service Manual, Page: 203 / 232

ASSEMBLY DRAWINGS: Theory Of Operation
Revision B Dash 3000/4000 Patient Monitor 9-15
2000966-105
Microprocessor
Supervisory Circuit,
Microcontroller Internal
Watchdog Timer The microprocessor supervisory circuit provides reliable operation of the
main processor board. This circuit monitors the +3.3 V power supply and
asserts a 140 mS active low reset pulse when the power supply voltage is
below +3.0 V during power-up and power-down conditions. A 3 V, 0.5 A
hour lithium battery is used to preserve the contents of two SRAM
devices and a real-time clock (RTC) when VCC is below the reset
threshold.
System Control Logic
The system ASIC contains all of the system control logic for the
Processor/Power Management PCB. Such functions include address
decoding, peripheral read and write control strobes, smart battery
control logic, display control, multiple I/O ports, and front panel key
switch debouncing.
Memory Eight Mb of non-volatile memory are provided to support the boot code
and expansion memory such as high resolution graphic trends data
storage. The 512 Kb boot block is write protected.
Four Mb of non-volatile memory are provided to support the main
software application code.
Four Mbytes of volatile memory are provided by the synchronous
graphics RAM. This memory is used for stack, variable storage,
dynamically allocated memory and video data storage.
One Mb of battery-backed SRAM supports storage of 24 hours of 1-
minute resolution patient trends, an error log containing 50 input errors,
and 50 output errors and storage for the CPM buffers.
The monitor configuration data such as Internet and Ethernet addresses,
unit name and bed number are maintained in the 2 Kb EEPROM. The
serial device resides on the I
2
C bus.
Real-Time Clock
The real-time clock incorporates an on-board quartz crystal. This feature
simplifies the design and eliminates adjustments. The time of day is
maintained to an accuracy of 15 seconds in 24 hours to support 24 hour
trend data. The RTC device is one of the devices on the I
2
C bus.
Audio Subsystem Audio tones are generated using a tone generator, an audio amplifier,
and an 8
Ω
, 2.5-in. speaker. The tone generator has built in D/A
converters and a mixer to generate the dual frequency tones.
Frequencies ranging from 150 Hz to 2800 Hz are produced.
Video Subsystem
The microprocessor contains a video controller that supports real-time
and non-real-time waveform drawing, menu drawing, and parameter
display.
Display brightness is controlled by a 50 k
Ω
digital potentiometer. The
potentiometer is interfaced to the brightness control input of an inverter.