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

Figure 3.6 Structure of the Error Frame [19].
From Figure 3.6, the Error Frame contains the following fields: Error Flag and Error
Delimiter Field. The Error Frame deliberately violates the bit stuffing rule (See Section 3.4
Error Detection and Handling – Stuff Error) by sending either six recessive bits or six dominant
bits in the Error Flag Field. The determination of whether the Error Flag is recessive or
dominant depends on the Error State of the node. There are two types of error flags: Active-error
and Passive-error flags. The Active-error flag consists of six consecutive ‘dominant’ bits and is
output by a node in an error-active state that detected an error. The Passive-error flag consists of
six consecutive ‘recessive’ bits unless it is overwritten by ‘dominant’ bits from other nodes. This
error flag is output by a node in an error-passive state when it detects an error. Depending on the
timing at which an error is detected by each node connected to the bus, error flags may overlap
one on top of another, up to 12 bits in total length. The Error Delimiter field is a sequence of
eight ‘recessive’ bits and indicates the end of the frame. After transmission of an Error Flag,
each node sends ‘recessive’ bits and monitors the bus until it detects a ‘recessive’ bit.
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