RT_Distance_2 Cumulative time and distance
RT_Distance_2: 128, 33 (0x802120 + unit id) (0x021)
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Byte 0: Validity
Bytes 1-3: Cumulative time (s)
Bytes 4-7: Cumulative distance (m)
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Cumulative time resolution is s/100.
Cumulative distance resolution is m/1000.
Distance message 2 gets held/reset by the triggers.