Posted on August 27, 2015 at 14:07All the SRAM used for receive filters is in CAN1, with a register setting to place the boundary between CAN1 and CAN2 filter groups. So as Clive points out CAN1 has to be enabled for the filter SRAM if you use CAN2, but CAN1 doesn't have to be assigned pins.
CAN is inherently a peer-to-peer network so there is no bus master per se controlling traffic, unlike what you normally find in an RS-485 network where one master controls line turnaround and slaves only respond to unicast requests.
However if you look for ''flying bus master'' in the CANopen protocol there is a bus master/slave pattern where the bus master coordinates system data object (SDO) transfers from many requesters to many responders. This has nothing to do with hardware.
Some CAN protocols also support redundant links (a big selling point for ST parts, many other vendors only put in one CAN interface). The CAN1 ''master'' is the primary link and CAN2 ''slave'' the redundant backup in case the CAN1 bus fails (cable short or open, dead transceiver, etc.). This can be critical where safety related processes are used. It's tough losing brakes in your car because the connector came loose on one of the CAN buses.....
Jack Peacock
