Mindray Passport 5-Lead, Service Manual

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Block Diagrams Theory of Operation
2 - 46 0070-00-0420 Passport 5-Lead, 5L, LT, XG Service Manual
There are two operation modes of the recorder: a trace mode and a graphics mode. In the
trace mode, the recorder prints at a fixed rate (e.g. 25mm/sec). And it will request data at its
own rate. If no data is supplied, the previous points will be repeated by the recorder.
Since the recorder needs data at a fairly high rate in trace mode, (up to 800 points per
second), the data rate will be controlled by the CPU. In other words, the CPU will only send
data to the recorder when it so chooses. The recorder will repeat points when it does not
receive data. In trace mode, the CPU should output data to the recorder at the front end
sampling rate: 286Hz.
Due to the relatively slow response time of the recorder (several microseconds), the IDMA
controller can be set up to control the writing of the recorder on a cycle steal basis. The
WRRDY* line is wired to the DREQ* line of the micro-controller. In other words, a DMA cycle
would be requested every time the recorder is ready to accept new data. When the
programmed number of transfers are complete, any further request from DREQ* would be
ignored. Note that the software must keep track of how much actual print data the recorder
can accept in text or graphics mode. This information is contained in the RSYNC* line (buffer
empty). In other words, the recorder interface software can only print on a line by line basis
via DMA.
The RCRST signal is used to reset the recorder. On power-up or reset, the signal would by
default put the recorder in a reset state.
Analog Front End Interface
The analog front end interface is an opto-isolated serial channel with data to and from the
front end processor. It currently runs at 115.2 K baud. This interface is connected to SCC1.
This is done to make the analog front end possess the highest priority interrupt. The CPU can
independently reset the front end processor using the FERST signal (port A bit 11). On power-
up or reset, the signal would by default put the front end processor in a reset state.
The analog front end is programmed to transfer a burst of analog data to the CPU at a
sampling rate of 286Hz. This rate is chosen to be a even multiple of the screen waveform
update rate (71.5 samples per second to give 25mm/sec). This sampling rate should be high
enough to capture the details of the ECG waveform.
External RS-232 Interface (optional)
Since the external RS-232 interface connects to external instruments, the communication
features, such as baud rate, parity, etc. are going to be programmable by the user. No CTS
and RTS signals are provided.
Optionally, an RS-485 interface can be installed. (A cut on the board is only necessary to
disconnect the RS-232 receive line.) The differential RS-485 lines are connected via a
bidirectional transceiver as a party line. The receiver is always enabled; the transmitter is
enabled by SEREN (port B pin 7). This line should normally be low to disable the transmitter.
This interface is connected to SCC2.