EmCan Protocol Specification

Bit Rate

No one bit rate can suite all applications.  Due to details of the collision detection mechanism in CAN, the bitrate limits the physical length of the bus.  The maximum CAN bitrate is 1 MHz, which is suitable for busses up to a few 10s of meters.  This would be suitable for a single industrial machine, but not for a large building.  Any one application will have its own tradeoff between bus length and data carrying capacity. 

While EmCan can not dictate a bitrate to suite all applications, it does recommend the default of 500 kHz when there is no specific reason for it to be different.  Any application-specific protocol layered on EmCan must clearly state the bit rate it will operate at.  Likewise, devices claiming compatibility with EmCan must clearly state the bitrate or bitrates they can operate at and how to select a different bit rate if the device is configurable. 

To attempt to simplify device configuration and limit the profusion of bit rates, the EmCan specification recommends (does not require) that applications use one of the following bit rates:

The maximum CAN bus length at 250 kHz bit rate is so long that other effects limit the bus length at lower bit rates.  In general, the recommended bit rates are 1 MHz divided by a power of 2.  If for some reason a slower bit rate than 250 kHz is needed, then it is recommended to use 125 kHz, 62.5 kHz, etc.