FMT1000 Datasheet, PDF (8/29 Pages) Fairchild Semiconductor – Motion Tracking Module with Output of Orientation, Inertial Motion Data and Magnetic Field

1.7.2 Xbus Protocol
The Xbus protocol is a proprietary protocol that allows
straightforward interfacing with the FMT1000-series.
Information about the Xbus protocol can be found in the
Low-Level Communication Protocol Documentation.
Section 6 provides a short introduction on the Xbus
protocol. It is advised to go read this short introduction
first before proceeding to the MTSSP explanation.
1.7.3 MTSSP Synchronous Serial Protocol
The communication protocol used for both I²C and SPI
is called MTSSP (MT Synchronous Serial Protocol).
Data Flow
MTSSP communication happens according the master-
slave model. The FMT1000-series module will always
fulfill the slave-role while the user/integrator of the
module is always the Master.
Communication is always initiated and driven by the
Master; the Master either writes data to the module or
the Master reads data from the module. The Master
sends messages to the module in order to control it.
These messages are reduced Xbus messages. A
reduced Xbus message is equal to a normal Xbus
message with the exception that preamble and BusID
are removed to save bandwidth. The calculation of the
checksum is done by assuming a BusID value of 0xFF
(master device).
The module needs time to process the control
messages it receives and will generate an acknowledge
message when ready. In order to get these
acknowledge messages at the Master the Master needs
to read them.
The following diagram shows data flow between Master
and module:
Figure 6. Data Flows within MTSSP
Data Ready Signal
The Data Ready Signal (DRDY) is a notification line
driven by the module. Its default behavior is to indicate
the availability of new data in either the notification- or
the measurement pipe. By default, the line is idle low
and will go high when either pipe contains an item.
When both pipes are empty the DRDY line will go low
Opcodes
again. The Master can change the behavior of the
DRDY signal.
The polarity can be changed to idle high, the output type
can be switched between push-pull and open drain. The
state of a specific pipe can be ignored. For example, it
can be configured that the presence of data in the
notification pipe won't influence the state of the DRDY
pin.
The following opcodes are defined.
Table 2. Opcodes for SPI and I²C
Opcode
Name
Read/Write
Description
0x01
ProtocolInfo
Read
Status of the protocol behaviour, protocol version
0x02 ConfigureProtocol
Write
Tweak the Protocol, e.g. the behaviour of the DRDY pin,
behaviour of the pipes
0x03
ControlPipe
Write
Used to send control messages to the module
0x04
PipeStatus
Read
Provides status information for the read pipes
0x05
NotificationPipe
Read
Used to read non-measurement data: errors acknowledgements
and other notifications from the module
0x06 MeasurementPipe
Read
All measurement data generated by the module will be available
in the measurement pipe
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FMT1000-series • Rev. 1.0
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