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IMU User Guide revision 3.1 SMC Ship Motion Control www.shipmotion.eu
4.6
ETHERNET PROTOCOLS
4.6.1
CHECKSUM CALCULATION
When checksum is being used in the Ethernet UDP protocols the motion sensor does calculate a
checksum using a 16-bit 1's complement checksum using RFC 1071 standard. The checksum is being
presented in the SMC header within the payload section.
In the checksum calculation the bytes 16 and 17 are excluded.
4.6.2
SMC ETHERNET PROTOCOL 1 UDP
The UDP datagram follows the standard RFC 768 format, below is the definition of the data fields
contained within the UDP datagram payload, each field consists of 4 bytes.
Note the field marked as the SMC header below is the header within the
payload
of the datagram
and must not be confused with the header of the UDP datagram itself. The payload is encoded in big-
endian.
The UDP 1 protocol uses the IEEE Standard 754 representation of the float numbers. In the output
message fields, no scaling for the motion sensor data is used when converting from Hex
representation to the float values.
Below is an example of the Motion Sensor, UDP 1 protocol, Hex data output. Payload only
53 4d 43 20 30 31 30 38 00 10 7a c0 39 39 00 01 ea 88 00 0e bf 1c 6c a1 40 93 2d d8 43 ac f8 8f 3c 16
7d 00 bc aa 50 00 bc f8 70 00 3a 8b ce 95 3c 9d ed df 3c 74 3a 69 bc 01 c4 bb 3c a6 ef d1 39 d6 4a ac
ba ef 80 80 bb b9 7d f0 b9 5d 21 60 bb bd 1f 6c 3b 79 89 9b 3b 2e 99 ed