Contec CMS50X Data Format
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Contents
Serial Port Settings
19200 baud, 8 data bits, 1 stop bit, odd parity.
Live Mode
In default "live" mode it spews a stream of data out, in a repeating 5 byte pattern (split into 2 packets.) Use an event driven handler to process this properly.. Polling code is possible but is a PITA (my original python one was used polling and sucked and had to resync all the time, but I didn't know about odd parity at the time..)
Code: Select all
[xx xx xx] [xx xx]
00 01 02 03 04
00 contains "flow control" and error information bitfield (bit 8 is always set, can be used to sync if using polling mode) 01 simple heartbeat plethysomogram (lower 7 bit) 02 even simpler pulse beat "thingy" (bit 0x40 is apparently the upper bit of the Pulse rate) 03 Pulse (lower 7 bits) 04 SpO2 (lower 7 bits)
Pay attention to the sequence as sometimes it can group packets together. (eg 5 byte packets, in either order, occasionally larger packet groups, but always in correct sequence)
To get at the stored recordings:
write a 2 byte sequence containing the codes "0xf5, 0xf5" read in 0x20 byte chunks until no more data, putting it all aside for later. write a 3 byte sequence containing "0xf6, 0xf6, 0xf6" to switch back to live mode.
Processing the recording data
data begins with the remainder of any live data packet, followed by sequence "0xf2 0x80 0x00" three times, followed by 3 or 4 bytes, followed by "0xf0 80 00" 5 or so times, followed by the actual data in 3 byte triplets
Example:
>F5 F5 [cruft] [recording data selected] [can be short] [can be short this may just be normal empty data] <[90 28 35 00] [F2 80 00 F2 80 00 F2 80 00] [80 81 72 00] [F0 80 00 F0 80 00 F0 80 00 F0 80 00 F0 80 00 F0 80 00] < F0 C4 5F F0 C3 5F F0 C8 5F F0 D4 5F... All data Triplets start with 0xf0, second byte's high bit is set. < lots more of the actual data... till it runs out. >F6 F6 F6
The 3 or 4 byte sequence after the "recording data selected" sequence is the length in bytes.. 7 bit values following the first 0x80.. flip the second bytes msb. high byte first. I'm still not sure why there sometimes is 4 bytes.. it could simply be more bits of the length (the last 7bit byte would be the high byte, as the data sequence begins with F0 anyway.)
Recorded Data is stored 1 pulse+spo2 pair per second. ie 1Hz.
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