Datasheet

msCAN12 Controller
M68HC12B Family Data Sheet, Rev. 9.1
258 Freescale Semiconductor
16.11.2 Identifier Registers
The Bosch CAN 2.0A and 2.0B protocol specifications allow for two different sizes of message identifiers.
The Bosch CAN 2.0A specification requires an 11-bit identifier in the message buffer and the Bosch CAN
2.0B specification requires a 29-bit identifier in the message buffer. The resulting message buffers are
referred to as standard and extended formats, respectively.
The identifier registers (IDRn) in the memory map can be configured to create either the 11-bit
(IDR10–IDR0) identifier necessary for the standard format or the 29-bit (IDR28–IDR0) identifier
necessary for the extended format. Figure 16-11 details the identifier structure used in the standard format
while Figure 16-12 details the identifier structure used in the extended format. ID10/ID28 is the most
significant bit and is transmitted first on the bus during the arbitration procedure. The priority of an
identifier is defined to be the highest for the smallest binary number.
Address
(1)
Register Name
01x0 IDENTIFIER REGISTER 0
01x1 IDENTIFIER REGISTER 1
01x2 IDENTIFIER REGISTER 2
01x3 IDENTIFIER REGISTER 3
01x4 DATA SEGMENT REGISTER 0
01x5 DATA SEGMENT REGISTER 1
01x6 DATA SEGMENT REGISTER 2
01x7 DATA SEGMENT REGISTER 3
01x8 DATA SEGMENT REGISTER 4
01x9 DATA SEGMENT REGISTER 5
01xA DATA SEGMENT REGISTER 6
01xB DATA SEGMENT REGISTER 7
01xC DATA LENGTH REGISTER
01xD TRANSMIT BUFFER PRIORITY REGISTER
(2)
01xE UNUSED
01xF UNUSED
1. x is 4, 5, 6, or 7 depending on which buffer, RxFG, Tx0,
Tx1, or Tx2, respectively.
2. Not applicable for receive buffers.
Figure 16-10. Message Buffer Organization