CAN Frequently Asked Questions

This CAN_FaqLinks page contains a collection of other FAQs on the web.

What is CAN?
- try to answer it here or see http://www.can-cia.org/can-knowledge/
What is the future of CAN ?
- CAN with flexible data rate - CAN FD - was introduced by Bosch in March 2012 on the 13th international CAN Conference
- CAN with eXtra Large payload - CAN XL - was introduced by Bosch in 2019
Why maintaining it this way?
- Because if many experts are contributing, the FAQ should be more precise and growing faster.
What is CAN with flexible Data Rate CAN FD
Where is CAN used?
- http://www.can-cia.org/can-knowledge/
When was CAN invented?
- http://www.can-cia.org/can-knowledge/can/can-history/
Who is Who in CAN ?
Where do I get the standards from?
- The only place is http://www.iso.ch , search for 11898-1
How does CAN work?
- http://www.can-cia.org/can-knowledge/
- An older CiA presentation describing the physical layer, can be found at http://weble.upc.es/asig/ea/practica4/CANphy.pdf
- Another CiA presentation describing the data link layer DLL http://weble.upc.es/asig/ea/practica4/CANdll.pdf
- Different CAN implementations in silicon are described in http://weble.upc.es/asig/ea/practica4/CANimpl.pdf
- CAN application fields http://weble.upc.es/asig/ea/practica4/CANappl.pdf
What kind of physical layer is used?
- Physical layer standards explained at CiA.
Why termination is needed and why it is 120 Ω
Why is my CAN not working ? Here are some Problem Solving Questions
What are Error Active, Error Passive, and Bus off of CAN Bus?
- read more: CAN Errors
What is the purpose of delimiters in CAN frame? HZ: The recessive formated delimiter bits are needed for resynchronization purpose of the nodes in one network by means of a falling edge. They surround the ACK bit which is send in recessive state by the transmitter and is overwritten by a dominant state by all receiving nodes that have sucessfully checked the CRC.
What are commonly used bit rates?
- read more: CAN FAQ Bitrates
Can a CAN Transceiver blow-up when connected to RS232?
- read more: Blow UP RS232
What is the difference between Basic CAN and Full CAN?
- read at CAN FAQ Basic-Full-CAN
What is TTCAN
- Time Triggered CAN - to make CAN more predictable. All you need to know at a first glance can be found at the sub heading Time-triggered communication on the following website: http://www.can-cia.org/can-knowledge/can/can-history/.
What connectors are used ? See CAN Connectors
- depends of the suggestions made in higher layer protocols. The most different kind of connectors and there pinning are described in the CiA paper CiA DR 303-1 V 1.1.1 part 1: CANopen Cabling and Connector Pin Assignment. Version 1.0 can be found at: http://www.datamicro.ru/can/standards/pdf/DR303-1.pdf
- Some can also be found directly here: http://www.cd-systems.com/Can/can-cables.htm
- Beware! Some manufacturers use proprietary pinning!
What is wrong with RTR ? using remote transmission requests
What is CAN message filtering ?
How is the BusOff handled by the CAN controllers?
What is the maximum CAN cable length ?
What is GMLAN ? General Motors CAN protocol. http://en.wikipedia.org/wiki/GMLAN
Is the filter for CAN messages before or after the receiver/ACK hardware?
- jk: ACK is always sent by all enabled nodes receiving a valid frame that are not the transmitter of the frame. Filtering only determines whether or not the received message gets stored in a mailbox, and for controllers with multiple filters, which mailbox. Filtering comes after the ACK is sent.
- pk: You may also have to set the acceptance filter much wider and do the final filtering in the software, the ACK mechanism would still not be an indication that someone is actually interested in your message.
What is Fault Tolerant CAN ?
- See ISO 11898-4

Bit Stuffing explanation.
I recently found this comment by Holger Zeltwanger:
The bit-stuffing rule reads, after five bits of the same value a bit of another value is stuffed in.

Original bit-sequence: 
000 11111 0000 1111 0000
Stuffed sequence: 
000 11111 (0) 0000 (1) 1111 (0) 0000 (1)
During de-stuffing, the CAN controller just counts the bits of the same value. Reaching five it deletes the next one.
Destuffed sequence: 000 11111 0000 1111 0000 (as the original sequence)