FMT1000 Datasheet, PDF (21/29 Pages) Fairchild Semiconductor – Motion Tracking Module with Output of Orientation, Inertial Motion Data and Magnetic Field

6 FMT1000-Series Settings and Outputs
The FMT1000-series module uses the proprietary Xbus protocol.
6.1 Message Structure
The communication with the MT is done by messages which are built according to a standard structure. The
message has two basic structures; one with a standard length and one with extended length. The standard length
message has a maximum of 254 data bytes and is used most frequently. In some cases the extended length
message needs to be used if the number of data bytes exceeds 254 bytes.
An MT message (standard length) contains the following fields:
Xbus header
Preamble
BID
MID
LEN
DATA
CHECKSUM
An MT message (extended length) contains these fields:
Preamble
BID
MID
LEN^ext
LEN
DATA
CHECKSUM
Table 16. Message Structure
Field
Field Width
Description
Preamble
1 byte
Indicator of start of packet  250 (0xFA)
BID
1 byte
Bus identifier or Address  255 (0xFF)
MID
1 byte
Message identifier
For standard length message:
- Value equals number of bytes in DATA field.
LEN
1 byte
- Maximum value is 254 (0xFE)
For extended length message:
- Field value is always 255 (0xFF)
EXT LEN
2 bytes
16 bit value representing the number of data bytes for extended
length messages. Maximum value is 2048 (0x0800)
IND ID
1 byte
The type of indication received
DATA (standard length)
0 – 254 bytes
Data bytes (optional)
DATA (extended length) 255 – 2048 bytes Data bytes
Checksum
1 byte
Checksum of message
Details on the Xbus protocol message structure can be found in the Fairchild MT Low Level Communication Protocol
documentation.
© 2015 Fairchild Semiconductor Corporation
FMT1000-series • Rev. 1.0
21
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