PXD10RM Datasheet, PDF (677/1332 Pages) Freescale Semiconductor, Inc – PXD10 Microcontroller

Table 18-4. Message Buffer Structure Field Descriptions (continued)
Field
Description
IDE
ID Extended Bit
This bit identifies whether the frame format is standard or extended.
1 = Frame format is extended
0 = Frame format is standard
RTR
Remote Transmission Request
This bit is used for requesting transmissions of a data frame. If FlexCAN 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 FlexCAN module treats it
as bit error. If the value received matches the value transmitted, it is considered as a successful bit
transmission.
1 = Indicates the current MB has a Remote Frame to be transmitted
0 = Indicates the current MB has a Data 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 Table 18-2). In reception, this field is written by the FlexCAN 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.
PRIO
Local priority
This 3-bit field is only used when LPRIO_EN bit is set in MCR and it only makes sense for Tx buffers.
These bits are not transmitted. They are appended to the regular ID to define the transmission
priority. See Section 18.4.3, Arbitration process.
ID
Frame Identifier
In Standard Frame format, only the 11 most significant bits (3 to 13) are used for frame identification
in both receive and transmit cases. The 18 least significant bits are ignored. In Extended Frame
format, all bits are used for frame identification in both receive and transmit cases.
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 18-5. Message Buffer Code for Rx Buffers
Rx Code
BEFORE
Rx New Frame
Description
0000
INACTIVE: MB is not active.
0100
EMPTY: MB is active and
empty.
Rx Code
AFTER
Rx New Frame
Comment
–
0010
MB does not participate in the matching
process.
MB participates in the matching process. When
a frame is received successfully, the code is
automatically updated to FULL.
Freescale Semiconductor
PXD10 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
18-7