Not all sensor network applications can deal with the wiring involved with a wireline CAN solution. Sometimes there is a just a gap that cannot easily be crossed with a wire. Other times it is just not practical, for example because the system is a temporary setup, which does not warrant clean installation of the wiring involved.
CAN-bus is really just intended a wire-based technology and must of it's features depend on the physical medium. However, if we don't bother too much about priorities and bus error features, then there is no reason not to route CAN-bus telegrams over a wireless medium. This is also acknowledged by CAN in Automation, the group behind CANopen, with their publications CiA 315 "Generic frame for wireless tunneling of CAN messages and for transfer of diagnostic data" and CiA 457 "CANopen interface profile wireless transmissions".
- Wireless networking for CAN-bus data
- Bridges operate as CANopen® device with device monitoring & configuration
- Transparent for J1939 or other 29-bit CAN applications
- Transparent for CAN-FD, FD can be disabled for individual bridges
- Supports up to 8 clients in the wireless domain in Layer-2 AP mode
- Supports encrypted point-to-point link in TCP/IP mode
- Configuration via CANopen or via PC application on micro-USB port
- Possibility for branding or custom firmware with specific behaviour
In Layer-2 mode, one bridge operates in access-point mode. The other bridges operate in station mode and connect to the AP-mode bridge. The default mode is Layer-2-AUTO, this starts the bridge in station mode and tries to connect to a access-point bridge. If no such bridge is found, then the device will become an access-point itself.
The TCP modes are for establishing a TCP/IP based link between two bridge devices. Because this uses standard TCP/IP, the bridges can connect to any WiFi access-point.
- Globally approved 2.4GHz ISM band using 802.11b/g/n protocol (Wi-Fi)
- CANopen® interface profile wireless transmission (CiA 457 + custom)
- Large FIFO buffers allow for buffering of bursts on either side
- Separate priority FIFO helps in preserving timing of messages with ID ≤ 0x100
- Supports LSS node ID assignment and Fastscan (CiA 305)
- Supports firmware update via wired or wireless CAN interface or locally via USB
- Supports power management & monitoring features (CiA 302-9 + custom for monitoring of bus voltage, input current, CPU voltage and CPU temperature)
- Supports custom heartbeat messages, using additional bytes for status
Wireless performance & limitations
Connecting CANopen devices over a wireless link strips some of the reliability and ruggedness features of the CAN bus protocol. Additionally, there are bandwidth limitations that are less easily defined than with a wireline approach.
Use of more than 2 bridge devices in a network results in multicast transmissions, which decreases effective bandwidth proportionally to the number of bridges. When the wireline feed bitrate and message rate exceeds the available RF bandwidth, increased message latency may occur and ultimately message loss.
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