Appendix A
A-2
Pulse Oximeter for Sleep Screening Operation Manual
Output Data format
Baud rate: 19200, 8 bits, one start, one stop, no parity check.
Data output starts in the Trend Printing Mode as soon as power is turned on.
Data transmission is unidirectional from the oximeter to the receiving device. The CTS (clear-
to-send) line from the receiving device to the oximeter can be used to control data flow.
After data pack has been sent, data communications stop, and can be resumed by cycling the
power of the oximeter.
Data pack consists of binary data. The overall structure of the pack is shown in the table below:
Byte 0
Least significant byte of the length of the data block (excluding check sum)
Byte 1
Most significant byte of the length of the data block (excluding check sum)
Byte 2
First byte of the data block
Byte 3
Second byte of the data block
Byte 4..
byte n
The rest of the data block
Byte n+1
Least significant byte of the check sum, which is the sum of all bytes in the data block
Byte n+2
Most significant byte of the check sum
As indicated in the table, each pack includes length, data block and check sum. Data in the
data block represents four-second samples.
Data blocked is compressed. The compression method is described below.
Each stored data byte is split into low and high nibbles, except for the cases described
later.
Each nibble can have a signed value in the range of -7 to 7. Bits 0 to 3 are used for SpO
2
,
bits 4 to 7 are used for the Pulse Rate.
To obtain the n+1-st value, the value of the corresponding nibble should be added to the
n-th value (considering sign).
Note: If n-th SpO
2
value is 96%, and bits 0 to 3 contain a signed –1 (0xf in HEX notation),
then the n+1-st value is 96% - 1 = 95%.
A special case is a byte 0x88 (88-hex). This byte is used for a marker. If this marker is found
in the byte sequence, the byte immediately following the marker byte is SpO
2
value in the
range 30 to 100 (value 255 means “no data”).
The byte immediately following SpO
2
is Pulse Rate in the range of 30 to 254 (value 255
means “no data”).
The next byte and all sequential bytes are the bytes divided into low and high nibbles,
until the next marker is found.
This method allows for almost 2:1 data compression rate.
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