Mindray DPM 1 Wartungshandbuch PDF herunterladen (Seite 14)

Circuit Principle

Pulse oximeter Service Manual 2-2

supply for IO module and analog circuit. The voltage of them is 3.3V.

S1C33209 has two crystal oscillators, OSC1 and OSC3. OSC1 supplies RTC and system

clock frequency, whose frequency is 32.768KHz. OSC3 supplies work frequency to the

CPU, whose frequency is 22.1184MHz.

2.1.1.2 Watchdog Circuit

The watchdog circuit control chip is MAX823. When S2 is shorted, the program will access

watchdog procedure. R64 and C63 compose RC low-pass filter to reduce interference of

the reset signal. R87 is a pull-up resistor. When power on or operate reset by manual, the

capacitor of C54 will release its charge and become low level voltage. C54 and R59 form

a RC low pass filter to reduce high frequency noise.

Fig 2-2 Watchdog Circuit

2.1.1.3 Data Storage

The DPM1 requires automatic data storage in case of power supply failure. 24WC64 IC

with the capacity of 8K bytes was adopted. This IC uses I

C bus.

The C111 and C112 act as filter capacitors to reduce the influence from high frequency

noise. When the 24WC64’s seventh pin is high level voltage, the IC is write-protected.

C113 is a filter capacitor between the write-protect pin and VDD pin. It is used to set the

write-protect pin to high level voltage to avoid wrong write operation. The circuit block is

shown as below:

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Mindray DPM 1 Wartungshandbuch Seite 14