Nellcor OXIMAX N-595 Service Manual page 122

Technical Discussion
114
The microprocessor is responsible for interacting with the analog front end,
and communicates with the front end through control signals. The
microcontroller receives the analog voltages from the front end analog-to-
digital (A/D) converters. The resultant data is used to calculate SpO
pulse rate values. The results are transmitted to the microprocessor via the
serial link.
The primary responsibilities of the microprocessor are:
• Digital signal processing of the front end data.
• Display of the SpO
including status light-emitting diodes (LEDs) on the membrane panel.
• User interface.
• Serial port communication through the SIP/SOP interface.
• Nurse call outputs.
• Analog outputs.
• Sound generation by generating the appropriate volume and
frequency control settings for the speaker circuitry.
• Monitoring and controlling pulse oximeter power.
• Communicating with the real-time clock (RTC).
• Communicating with the electrically-erasable-programmable-read-
only-memory (EEPROM).
• Trend data collection and storage.
Static random-access-memory (RAM) and FLASH read-only-memory
(ROM) are provided for the microprocessor on the PCB. Two systems pulse
oximeter integrated circuits (ICs) on the main PCB Vcc (+5 volts) and +3.3
volts) power supply and provide watchdog timer. The system monitor will
reset the entire PCB if the +5 volts is out of tolerance or the watchdog timer is
not periodically reset by the software.
The FE-102 front end also contains a Static RAM, FLASH ROM, and a
system monitor. The FE-102 front end's system monitor will reset just the FE-
102 front end if the 5-volt VCCA is out of tolerance or the watchdog timer is
not periodically reset by the software.
Power is supplied to the N-595 either from an AC connection (110 or 220
VAC) or from a 6-volt, 4 ampere-hour battery. The transition between power
sources is invisible to the user, from AC power to battery power or from
battery power to AC power. This allows functionality to remain during cases
where AC power is lost or applied. The microprocessor monitors the battery
voltage and shuts off the unit power supply if the battery voltage becomes too
low to support N-595 functionality. The FE-102 front end power supply for
the N-595 is an isolated switcher which generates +5 volts and ±12 volts.
and pulse rate data, and all other display data
2
and
2