Mindray Passport 5-Lead, Service Manual

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Block Diagrams Theory of Operation
2 - 58 0070-00-0420 Passport 5-Lead, 5L, LT, XG Service Manual
Microcontroller
The microcontroller manages the flow of data between the host and the Novametrics
Capnostat. It consists of a 68HC705 OTP single chip microcontroller. It operates at an
oscillator frequency of 3.6864 MHz, obtained from the network including crystal Y1, bias
resistor R1, and loading capacitors C1 and C2. The oscillator also provides clocking for U4.
When it is brought out of reset, an internal self test is performed, which verifies the PROM
contents and RAM operation. During this self test period, lasting several ms, bit 4 of port C is
configured as an output and driven low. This asserts reset to the Capnostat. At the conclusion
of the self test, this pin is reconfigured as an input, releasing the Capnostat reset, which is
designed for an open-collector interface. The start-up of the Capnostat and CIM are thus
synchronized.
Any data written to the CIM data port is accepted by the microcontroller on port B. Data to
be sent to the host is asserted on port A. Communications with the Capnostat take place by a
CMOS level asynchronous serial link in J92. The parameters are 9600 baud, 8 data bits, no
parity, and one stop bit, with the data having “true” polarity.
Two locations for optional jumper links are provided. They can be read on bits 6 and 7 of
port C. Jumper JP2 is reserved for future options. If JP1 is present a special test code is
invoked immediately after reset.
Power Converter
The CIM also supplies operating power to the Capnostat. Power connections are made via
J92 and J94. The +5 volts and digital ground obtained from the ISA bus are used to supply
logic power. The +5 rail used to power the Capnostat II through a dropping resistor R2, also
powers a heater in the Capnostat. The Capnostat II and III also requires dual 15 volt and 12
volt supplies respectively. However, it draws large transient currents from these rails, making
it undesirable to operate the Capnostat from the host’s 15 volt analog supplies. Therefore, the
CIM includes a commercial DC-DC converter module, VC1, which supplies these
requirements. The converter is powered from the raw bulk supply, obtained from J93.
Capacitor C10 reduces the reflected load transients. A converter capable of supplying the
peak Capnostat load currents would be quite large. For this reason, the converter is sized
closer to the average requirements, with a filter consisting of C9 and L2 providing smoothing
of these peaks. The Capnostat III also requires a -12V linear supply. This is derived from a -
12V regulator, U5.
Interface Connectors
The CIM is capable of interfacing to either a Capnostat II or III. Unfortunately, the 2 modules’
interface connector have different signal definitions. In order to prevent the possibility of the
wrong module being plugged into the CIM, 2 connectors were specified. One is for the
Capnostat II (J92) and one is for the Capnostat III (J94). They differ in that the Capnostat II
uses a 15 V supply and also has a separate 5V heater supply, while the Capnostat III uses a
dual 12V supplies.