Freescale’s Scalable Controller Area Network (S12MSCANV3)
MC9S12XHY-Family Reference Manual, Rev. 1.01
366
Freescale Semiconductor
11.3.3
Programmer’s Model of Message Storage
The following section details the organization of the receive and transmit message buffers and the
associated control registers.
To simplify the programmer interface, the receive and transmit message buffers have the same outline.
Each message buffer allocates 16 bytes in the memory map containing a 13 byte data structure.
An additional transmit buffer priority register (TBPR) is defined for the transmit buffers. Within the last
two bytes of this memory map, the MSCAN stores a special 16-bit time stamp, which is sampled from an
internal timer after successful transmission or reception of a message. This feature is only available for
transmit and receiver buffers, if the TIME bit is set (see
Section 11.3.2.1, “MSCAN Control Register 0
(CANCTL0)
”).
The time stamp register is written by the MSCAN. The CPU can only read these registers.
1. Read: Anytime
Write: Anytime in initialization mode (INITRQ = 1 and INITAK = 1)
Table 11-25. CANIDMR4–CANIDMR7 Register Field Descriptions
Field
Description
7-0
AM[7:0]
Acceptance Mask Bits — If a particular bit in this register is cleared, this indicates that the corresponding bit in
the identifier acceptance register must be the same as its identifier bit before a match is detected. The message
is accepted if all such bits match. If a bit is set, it indicates that the state of the corresponding bit in the identifier
acceptance register does not affect whether or not the message is accepted.
0 Match corresponding acceptance code register and identifier bits
1 Ignore corresponding acceptance code register bit
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