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MPC5566 Microcontroller Reference Manual, Rev. 2
22-8
Freescale Semiconductor
RTR
Remote transmission request. This bit is used for requesting transmissions of a data frame. If
FlexCAN2 transmits this bit as ‘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
FlexCAN2 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
LENGTH
Length of data in bytes. This 4-bit field is the length (in bytes) of the RX or TX data, which is located
in offset 0x8 through 0xF of the MB space (see
). In reception, this field is written by the
FlexCAN2 module, copied from the DLC (data length code) field of the received frame. In
transmission, this field is written by the CPU and corresponds to the DLC field value of the frame
to be transmitted. When RTR = 1, the Frame to be transmitted is a remote frame and does not
include the data field, regardless of the length field.
TIME STAMP
Free-running counter time stamp. This 16-bit field is a copy of the free-running timer, captured for
Tx and Rx frames at the time when the beginning of the Identifier field appears on the CAN bus.
ID
Frame identifier.
• Standard frame format: the 11 (3:13) most significant bits (MSB) are the frame ID in receive and
transmit frames. The 18 (14:31) least significant bits (LSB) are ignored.
• Extended frame format: all bits are the frame ID in receive and transmit frames.
DATA
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 the CAN bus. For TX frames, the CPU prepares the data field to be transmitted
within the frame.
Table 22-5. Message Buffer Codes for RX Buffers
RX Code before
RX Frame
Description
RX Code after
RX Frame
Comment
0000
NOT ACTIVE: MB is not active.
—
MB does not participate in the matching process.
0100
EMPTY: MB is active and
empty.
0010
MB participates in the matching process. When a frame
is received successfully, the code is automatically
updated to FULL.
0010
FULL: MB is full.
0010
The act of reading the C/S word followed by unlocking the
MB does not make the code return to EMPTY. It remains
FULL. If a new frame is written to the MB after the C/S
word was read and the MB was unlocked, the code still
remains FULL.
0110
If the MB is FULL and a new frame is overwritten to this
MB before the CPU had time to read it, the code is
automatically updated to OVERRUN. See
Section 22.4.3.1, “Matching Process
for details about
overrun behavior.
Table 22-4. Message Buffer Field Descriptions (continued)
Name
Description
Summary of Contents for MPC5566
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