3-8 V60 Ventilator Service Manual 1049766 Rev A
Chapter 3: Theory of Operation
3.2.4 CPU PCBA
• Microprocessor: once in a run state, the microprocessor can only be
reset by a watchdog timeout or out-of-specification power condition.
Monitors operation of the ventilator and controls delivery of air and
oxygen to the patient. Verifies safe ventilator operation.
• Flash memory: 8 MB program storage.
• RAM: 8 MB for program execution and volatile data storage.
• EEPROM: 4 KB of storage for board-specific information (including
operating hours, time since last service, serial numbers, part
numbers, and software and hardware revisions).
• Watchdog timer: disables the blower and oxygen flow if not strobed by
software within a predefined time window that is independent of the
CPU master clock. In addition, ensures that software is operating.
• Real-time clock (RTC): a time of day clock that provides the date and
time to the ventilator, and is powered by a dedicated 3-V lithium coin
cell battery.
• LCD interface supports a display of 1024 horizontal x 768 vertical
pixels in 256 colors with a refresh rate of at least 50 Hz. The CPU
PCBA controls LCD brightness by varying a control voltage over a
range of 0 to 3.5 V (minimum to maximum brightness).
• Touch screen interface supports a five-wire type touch screen.
• Nav-ring rotary adjustment interface with a minimum resolution of 24
ticks per revolution.
• User key switches: interfaces to front panel keys.
• Alarm subsystem: includes a speaker driver circuit for the two main
speakers, a backup piezo alarm, and a three-wire relay-controlled
remote alarm interface (normal open, NO, or normal closed, NC) on
the ventilator back panel.
• Blower speed monitor measures blower speeds from 3,000 to 50,000
RPM with 2% accuracy.
• Electrical interfaces to the power management (PM) and motor
controller (MC) PCBAs.
• Two USB ports and an ethernet connection are designed for future
enhancements. Table 3-1 summarizes hospital information system
(HIS) RS-232 port pinout.
CPU PCBA
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