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9.3
DEFINITION OF TERMS
Main PCB
Microprocessor
Figure 9-6: Printer Control Block Diagram
Analog to Digital (A/D) converter. The CPU has a 10-bit A/D converter on
board. Up to eight different analog inputs can be provided to the A/D converter
for measurement.
Central Processing Unit (CPU). An Intel 80C196KC 16-bit microcontroller.
The CPU sends and receives control signals to the SpO
and optional printer.
Content Addressable Memory (CAM). The CPU controls the HSO lines with
the CAM. CAM is controlled by software and programmed with events
scheduled relative to one of two internal timers.
High Speed Outputs (HSO). The 6 HSO lines control most of the timing of the
LED signal pulse and the demodulation of the received signal.
Input and Output (I/O). Digital lines that are used by the CPU to read in data
and output data.
Light Emitting Diodes (LEDs). Two LEDs are used in Nellcor oximetry
sensors. Light is transmitted through body tissue and received by a
photodetector circuit that converts it to photocurrent. The two wavelengths,
which are used for calculation of pulse rate and oxygen saturation in blood, are
transmitted at the following frequencies:
•
infrared (IR) light at approximately 915 microns
•
red light at approximately 660 microns
Pulse Width Modulation (PWM). The three 8-bit PWM outputs can be
software controlled; their duty cycle can be changed from 0-255/256 of the total
pulse duration. PWM frequency is the crystal frequency of the CPU, which is 10
MHz divided by 1024. The PWMs control the gains within the analog circuit.
RCal. Sensor RCal value is a resistance value specific to an individual sensor.
This value is used by the software during oxygen saturation computations to
maximize accuracy.
Real-Time Clock (RTC). The RTC is used with the optional printer to track
time and date for printouts.
AUX PCB
Printer
interface
Technical Supplement
Printer
flex
circuit
PCB
User push buttons
On
ADV
D/D
analog section, display,
2
Printer
9-5
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