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IMU383 Series User's Manual
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Reads default non-volatile fields
G = get
Gets current volatile fields or settings
W = write
Writes default non-volatile fields. These fields are stored in non-volatile memory and
determine the unit's behavior on power up. Modifying default fields take effect on the
next power up and thereafter.
S = set
Sets current volatile fields or settings. Modifying current fields will take effect
immediately by modifying internal RAM and are lost on a power cycle.
5.3.3
Payload Length
The payload length is always a one byte unsigned character with a range of 0-255. The payload
length byte is the length (in bytes) of the <variable length payload> portion of the packet
ONLY, and does not include the CRC.
5.3.4
Payload
The payload is of variable length based on the packet type.
5.3.5
16-bit CRC-CCITT
Packets end with a 16-bit CRC-CCITT calculated on the entire packet excluding the 0x5555
header and the CRC field itself. A discussion of the 16-bit CRC-CCITT and sample code for
implementing the computation of the CRC is included at the end of this document. This 16-bit
CRC standard is maintained by the International Telecommunication Union (ITU). The highlights
are:
Width = 16 bits
Polynomial 0x1021
Initial value = 0xFFFF
No XOR performed on the final value.
See Appendix B for sample code that implements the 16-bit CRC algorithm.
5.3.6
Messaging Overview
Table 26 summarizes the messages available by IMU383 Series model. Packet types are assigned
mostly using the ASCII mnemonics defined above and are indicated in the summary table below
and in the detailed sections for each command. The payload byte-length is often related to other
data elements in the packet as defined in the table below. The referenced variables are defined in
the detailed sections following. Output messages are sent from the IMU383 Series inertial system
to the user system as a result of a poll request or a continuous packet output setting. Input
messages are sent from the user system to the IMU383 Series inertial system and will result in an
associated Reply Message or NAK message. Note that reply messages typically have the same
<2-byte packet type (U2)> as the input message that evoked it but with a different payload.
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