Mindray Passport 5-Lead, Service Manual

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Block Diagrams Theory of Operation
2 - 26 0070-00-0420 Passport 5-Lead, 5L, LT, XG Service Manual
Signal Data Isolation
The signal data isolation block provides communication across the patient isolation barrier.
Serial data originating at the microcontroller’s TDO pin is inverted by one section of U36. It
is then buffered, and inverted again, by transistor Q10 and R230, which operate as a
saturated switch. The collector circuit of Q10 includes the LED of optocoupler U42 and
current limiting resistor R229. The TDO pin idles at a logic high state, and has bursts of low
level pulses during actual data transmission, which occurs at a low duty cycle. The driver
configuration used results in the LED being “off” most of the time, conserving power. The
optocoupler, U42, provides the actual isolation. The optocoupler features a separate
photodiode and amplifier transistor, providing the good high frequency response required to
support the 115.2 K baud data rate. On the non-isolated side, the open-collector output of
U42, together with pullup resistor R233, produce a CMOS logic compatible signal. This
signal has the same polarity as that on the TDO pin, and is routed to the Control Module
CPU via J42 pin 3.
Serial data originating at the Control Module CPU is connected to J42 pin 4. Transistor Q13,
R235, and R238 are used to invert this data, which is then buffered and inverted again by
Q11. The collector circuit of Q11 contains the LED of optocoupler U43 and current limiting
resistor R234. Note that U43 is driven in the same way as U42, described above. On the
isolated side, the open collector output of U43, together with pullup resistor R231, produce a
CMOS compatible signal, which is connected to the RDI input of the microcontroller, U38.
The Control Module CPU can cause a reset of the front end microcontroller by asserting a
logic high level on J42 pin 5. Via R237, this signal will saturate Q12. The collector circuit of
Q12 contains the LED of optocoupler U14 and current limiting resistor R236. Thus, the
optocoupler is turned “on” when the reset signal is asserted. On the isolated side, the
optocoupler transistor then pulls the RESET pin of the microcontroller low, against pullup
resistor R232. When the Control Module CPU returns J42 pin 5 to a low level, the RESET pin
will go high and microcontroller operation will begin.
2.2.3 SpO
2
Board
Overview
SpO2 board consists of analog and digital sections. Analog section provides all the patient
finger probe excitation and analog signal processing. Digital section controls the operation
of analog part of the board and shares its RAM with an external processor via ISA bus.
A pulsatile arterial saturated oxygen monitor detects the oxygenation level of the blood in the
body’s arterial circulation. It is used to continuously monitor the effectiveness of the
pulmonary system (lungs). Specifically the device, within limits, determines the fraction of
hemoglobin molecules carrying oxygen from the lungs to the body cells. Termed % SPO2,
this fraction is normally about 97 percent.