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

Recently, a technique has been proposed to use two reserved bits of the CAN extended
data frame identifier field as part of an initial address assignment process [40]. The CAN
protocol has two reserved bits in the Control Field for future expansion and/or modifications to
the existing protocol. CAN 2.0B specification requires a transmitting node to transmit these
reserved bits as zeros (dominant state). However, when a receiving unit receives the message, it
will ignore the state of these two bits. The method proposed in [40] is to use these reserved bits
to represent the address claim status of a CAN node as shown in Table 4.1.
Table 4.1 Address claim status and reserved bits [40].
Reserved bits Meaning
00 Address Acquired (Normal Tx)
01 Address Assignment Pending
10 Address Claim Override
11 Reserved
Additionally, the CAN Controller for each node should be modified as shown in Figure
4.7 to include an additional unit for address claim. This unit should include special registers
which will contain the highest priority of the message that will be transmitted from the node and
node address. A timing control unit is also required for monitoring the address claim timeout
and a priority resolving unit will resolve address claim contentions.
Figure 4.7 Address Claim Unit [40].
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