Freescale Semiconductor MCF5329 Reference Manual page 582

FlexCAN
Field
31–28 Reserved, must be cleared.
27–24 Message buffer code. Can be accessed (read or write) by the CPU and by the FlexCAN module itself, as part of
CODE the message buffer matching and arbitration process. The encoding is shown in
Section 23.3.10, "Functional Overview,"
23 Reserved, must be cleared.
22 Substitute remote request. Fixed recessive bit, used only in extended format. It must be set by the user for
SRR transmission (Tx Buffers) and is stored with the value received on the CAN bus for Rx receiving buffers. It can be
received as recessive or dominant. If FlexCAN receives this bit as dominant, then it is interpreted as arbitration loss.
0 Dominant is not a valid value for transmission in Extended Format frames
1 Recessive value is compulsory for transmission in Extended Format frames
21 ID extended bit. Identifies whether the frame format is standard or extended.
IDE 0 Standard frame format
1 Extended frame format
20 Remote transmission request. Used for requesting transmissions of a data frame. If FlexCAN transmits this bit as
RTR 1 (recessive) and receives it as 0 (dominant), it is interpreted as arbitration loss. If this bit is transmitted as 0
(dominant), then if it is received as 1 (recessive), the FlexCAN module treats it as bit error. If the value received
matches the value transmitted, it is considered as a successful bit transmission.
0 Indicates the current MB has a data frame to be transmitted
1 Indicates the current MB has a remote frame to be transmitted
19–16 Length of data in bytes. Indicates the length (in bytes) of the Rx or Tx data; data is located in offset 0x8 through
LENGTH 0xF of the MB space (see
DLC (data length code) field of the received frame. DLC is defined by the CAN Specification and refers to the data
length of the actual frame before it is copied into the message buffer. In transmission, this field is written by the CPU
and is used as the DLC field value of the frame to be transmitted.
When RTR is set, the frame to be transmitted is a remote frame and is transmitted without the DATA field, regardless
of the LENGTH field.
15–-0 Free-running counter time stamp. Stores the value of the free-running timer which is captured when the beginning
TIME of the identifier (ID) field appears on the CAN bus.
STAMP
31–29 Reserved, must be cleared.
Standard frame identifier: In standard frame format, only the 11 most significant bits (28 to 18) are used for frame
identification in receive and transmit cases. The 18 least significant bits are ignored.
28–0
ID
Extended frame identifier: In extended frame format, all bits (the 11 bits of the standard frame identifier and the 18
bits of the extended frame identifier) are used for frame identification in receive and transmit cases.
31–24, Data field. Up to eight bytes can be used for a data frame. For Rx frames, the data is stored as it is received from
23–16, the CAN bus. For Tx frames, the CPU provides the data to be transmitted within the frame.
15–8, 7–0
DATA
23-18
Table 23-11. Message Buffer Field Descriptions
Description
for additional information.
Figure 23-13). In reception, this field is written by the FlexCAN module, copied from the
MCF5329 Reference Manual, Rev 3
Table 23-12 and Table 23-13. See
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