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20.1.2.3 Error Frames
An Error Frame is generated by any node that detects a bus error. An Error Frame
consists of two fields, an Error Flag field followed by an Error Delimiter field. The Error
Delimiter Field consists of 8 recessive bits and allows the bus nodes to restart bus
communications after an error. There are, however, two forms of Error Flag fields. The
form of the Error Flag field depends on the error status of the node that detects the error.
When an error-active node detects a bus error, the node generates an Error Frame with
an active-error flag. The error-active flag is composed of six consecutive dominant bits
that actively violate the bit-stuffing rule. All other stations recognize a bit-stuffing error
and generate Error Frames themselves. The resulting Error Flag field on the CAN bus
therefore consists of six to twelve consecutive dominant bits (generated by one or more
nodes). The Error Delimiter field completes the Error Frame. After completion of the
Error Frame, bus activity returns to normal and the interrupted node attempts to re-send
the aborted message.
If an error-passive node detects a bus error, the node transmits an error-passive flag
followed, again, by the Error Delimiter field. The error-passive flag consists of six
consecutive recessive bits, and therefore the Error Frame (for an error-passive node)
consists of 14 recessive bits (i.e. no dominant bits). Therefore, the transmission of an
Error Frame by an error-passive node will not affect any other node on the network,
unless the bus error is detected by the node that is actually transmitting (i.e. the bus
master). If the bus master node generates an error-passive flag, this may cause other
nodes to generate Error Frames due to the resulting bit-stuffing violation. After
transmission of an Error Frame an error-passive node must wait for 6 consecutive
recessive bits on the bus before attempting to rejoin bus communications.
Bus Idle
Bus Idle
Figure 20-3 CAN Error Frames
User's Manual
MultiCAN, V2.24
Controller Area Network Controller (MultiCAN)
Error Frame of "Error Active" Node
6
6
Error Frame of "Error Passive" Node
8
Bus Idle
Error Delimiter Field
Error Flag Field
8
Bus Idle
20-7
TC1728
Recessive Level
Dominant Level
Recessive Level
Dominant Level
MCT06260
V1.0, 2011-12
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