TotemBUS modules

Functionality extension modules for RoboBoard X4. Each one has a set of features, that become available once module is connected over TotemBUS cable. It's an easy way to enrich your project without any tinkering or looking for compatible libraries. Each module has documented objective API code to control all its capabilities.

Module number

Every module has number [XX] printed in a white square to identify its type and to find documentation. Same number is used when writing the code.

Module serial

There is unique serial identifier in case more than one module with the same number exists within TotemBUS network. A command can be sent to a specific module matching its serial number. It isn't visible anywhere on the board and must be acquired programmatically.

Module revision

Version tag (v1.0) identifies board revision. Each one may have some hardware changes or new functionality. Firmware is versioned separately.

Connecting modules

Modules are daisy-chain connectable with a 6 pin connector. It provides power and communication. Some modules (boards like X3 and X4) has BLE interface and can connect to TotemBUS network wirelessly instead of a physical cable. This is mostly used to control modules from a smartphone. Module is operational the second it's physically connected to TotemBUS network and powered on.

Controlling modules

Each module accepts a set of commands to control their specific capabilities (like reading sensor data, controlling lights or motors). Controller can also subscribe to data in order for module to start broadcasting it. The list of available functions can be found in documentation page for specific module.

TotemBUS protocol

TotemBUS is our implemented communication protocol to control Totem modules over CAN bus network. It is designed to overcome limitations of similar systems and offer new ways of building robots. The key factors are fast response, low overhead, higher power and easy programming. Communication is peer-to-peer, so modules can respond any time, unlike I2C alternatives (compare to Qwiic). This gives more flexibility in module functionality and communication types.

This protocol utilizes advantages of CAN bus addressing. Each module has embedded number and serial that is sent over the network. Using this technique, single message can be sent to a specific module or group of them. Every device on the bus can see what is happening and intercept information.
As CAN bus itself is robust communication protocol, it can only transfer 8 bytes of data in single frame. Here comes TotemBUS protocol to wrap all module functionality and encode it to simple CAN frames. There are similar protocols available (e.g. CANopen), but our solution is designed for maximum efficiency in this use case.

Modules accept string based messages (similar as MQTT) that are encoded to 32bit number, for communication efficiency. Each message can pass a variable length and format parameter. This saves a lot of bandwidth and increases response time. Protocol also implements reading (polling), broadcasting and subscription mechanism. This is used to remove some strain from host device and leave communication line less cluttered with only mandatory data sent.

Comparison to Qwiic

	TotemBUS	Qwiic
Connector	6-pin micro match	4-pin JST
Wire length	100M	1M
Voltage	5V and 12V	3.3V
Current	1A	226mA
BUS name	CAN	I2C
BUS type	peer-to-peer	master-slave
Speed	500 kb/s	100 kb/s or 400 kb/s*
Protocol	TotemBUS	module specific
API	included	library per module
Daisy-chain	yes	yes
Data pooling	yes	yes
Data braodcast	yes	no
Events (interrupt)	yes	no
X4 as slave	yes	no
Use same modules	yes	no**

*  Some modules can be configured with higher speed.
** Identical modules on single line can be used only if they support I2C address change.