
msCAN12 Controller
Data Sheet
M68HC12B Family — Rev. 9.0
280
msCAN12 Controller
MOTOROLA
All bits of the 13-byte data structure are undefined out of reset.
NOTE:
The receive buffer can be read anytime but cannot be written. The transmit buffers
can be read or written anytime.
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