GE Dash 3000 Service Manual page 51

Real-time clock
Audio subsystem
Video subsystem
Analog outputs
Defib Sync
2000966-542D
Equipment overview: Theory of operation
The real-time clock incorporates an on-board quartz crystal. This feature
simplifies the design and eliminates adjustments. The time of day on a
standalone patient monitor is maintained to an accuracy of 15 seconds in
24 hours to support 24 hour trend data. The RTC device is one of the
2
devices on the I C bus.
Audio tones are generated using a tone generator, an audio amplifier,
and an 8, 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.
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 digital potentiometer. The
potentiometer is interfaced to the brightness control input of an inverter.
Two analog output channels support ECG and BP. The pace pulse is
generated on the main processor board and inserted into the analog out
ECG signal. The digital-to-analog conversion for both ECG and blood
pressure output signals are performed on the main processing board via
a two channel 12-bit serial DAC. Cal data is stored on the processor/
power management PCB.
The QRS complex of ECG data acquired from the DAS generates the
marker-out signal. A software selectable pulse width and pulse
amplitude is provided in the Boot Loader Menu.
Dash 3000/4000/5000 2-31