DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

Stuff Error – To verify a Stuff Error, six consecutive bits with the same polarity are
inserted in a CAN message between the Start of Frame and the CRC Delimiter. This
causes a Stuff Error to occur and after ten bit time slots the message is resent with
random dominant and recessive bits between the two delimiters.
Error – Active Error State – Since this is normal operation as long as the Transmit Error
Counter (TEC) and Receive Error Counter (REC) are below 128, no test is necessary to
prove proper operation. If the TEC or REC exceeds 127, the nodes become either Error –
Passive or go in to the Bus – Off state.
Error – Passive Error State – A node becomes Error – Passive when either the TEC or
REC exceeds 127. Error – Passive nodes are not permitted to transmit Active Error Flags
on the bus, but instead, transmit Passive Error Flags, which consist of six recessive bits.
To verify this state, the REC and TEC are set to random values above 127 but less than
255. This forces the nodes to enter the Error-Passive state and transmit a Passive Error
Flag (six recessive bits). At this point a dominant bit is sent on the bus, which is seen by
the Error – Passive nodes, and forces these nodes to see the bus as being idle for eight
additional bit times after an intermission frame before recognizing the bus as available.
After this time, the nodes begin retransmitting normally and return to the Error-Active
state.
Bus – Off – This test is an extension of the test performed in Section 5.3.21.1. To verify
nodes being in the Bus-Off state, a value of 256 is placed in the TEC, since receive errors
cannot cause nodes to go Bus-Off. While in this mode the nodes cannot send or receive
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