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can [2018/12/28 21:03]
69.120.156.156 		can [2019/03/31 14:49] (current)
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- ====== Controller Area Network ======+====== Controller Area Network ======
  
 ===== Overview ===== ===== Overview =====
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 ===== CAN Frame ===== ===== CAN Frame =====
  
-{{ :can-bus-frame_in_base_format_without_stuffbits.svg |}}+There are 4 types of CAN Frames 
 +  * **Data Frame** - data transfer from one sending node to one or numerous receiving nodes 
 +  * **Remote Frame** - any node may request data from one source node. A remote frame is followed by the requested data. 
 +  * **Error Frame** - any node may signal an error condition at any time during a data or remote frame transmission 
 + 
 +{{ ::can-bus-frame_in_base_format_without_stuffbits.png?direct&600 |}}
  
 The distance between frames is a minimum of 3 bit times. The distance between frames is a minimum of 3 bit times.
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 The dominant level (TTL = 0V) always overrides a recessive level (TTL = 5V). This is important during bus arbitration.  The dominant level (TTL = 0V) always overrides a recessive level (TTL = 5V). This is important during bus arbitration. 
  
-{{:img_1492.jpg?400|}}+{{ :can_open_collector.png?direct&400 |}} 
 + 
 +A remote frame requests the transmission of a message by another node. This type of message is uncommon and CiA says to avoid its usage. 
 + 
 +A lower message ID number represents a high message priority. 
 + 
 +==== Acknowledgement Field ==== 
 + 
 +The acknowledgement field serves as a confirmation of a successful CRC check by the receiving nodes in the network. 
 + 
 +==== Error Checking ==== 
 + 
 +CAN implements a robust and elegant error checking system that allows for: 
 +  * Retransmission of frames that did not pass a 15 bit [[CRC]] check by a receiving node 
 +  * Detection of bus fault by a transmitting node by monitoring the bus after every bit cycle and ensuring the bus level is equal to intended transmission bit 
 +  * Allows a node to determine whether or not it was the first error reporting node, which allows the determination and removal of a defective node. 
 + 
 +==== Transmission Times ==== 
 + 
 +A CAN frame has a minimum of 47 bits (no bit stuffing and no data) and a maximum of 135 bits (max bit stuffing and 8 bytes of data) 
 + 
 +Maximum number of messages with average bit stuffing at 1 MBit and 8 bytes is 8,771 per seconds and 17,543 per second with 1 data byte. 
 + 
 +==== Data Transfer Synchronization ==== 
 + 
 +CAN uses Non-Return-to-Zero bit encoding. This provides highest transport capacity but requires bit stuffing. In CAN synchronization is done with the SOF bit, which marks the start of a frame, and by bit stuffing, by only allowing 5 consecutive bits of the same polarity.  
 + 
 + 
 +==== Wire Length ==== 
 + 
 +The wire lengths are as follows:  
 + 
 +{{ ::rtaimage.jpg?direct&400 |}} 
 + 
 +==== Implementation ==== 
 + 
 +Here is a chip implementation:(([[https://www.analog.com/media/en/technical-documentation/application-notes/AN-1123.pdf |Analog Devices Controller Area Network (CAN) Implementation Guide]]))  
 + 
 +{{ :can_stuff.png?direct&400 |}} 
 + 
 +==== Notes ==== 
 + 
 +ECAN is the "Enhanced Controller Area Network" module from Microchip. It's what they call they module that is compatible with everything up to CAN2.0B (which is the latest CAN standard up that includes the 29 bit extended identifier). (([[http://ww1.microchip.com/downloads/en/devicedoc/70226c.pdf|Microchip's ECAN module]])) 
 + 
  
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