K60P100M100SF2RM Datasheet, PDF (1358/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional Description
Table 48-114. Composition of the arbitration value when Local Priority is disabled
Format
Standard (IDE = 0) Standard ID (11
bits)
Extended (IDE = 1) Extended ID[28:18]
(11 bits)
Mailbox Arbitration Value (32 bits)
RTR (1 bit)
IDE (1 bit)
- (18 bits)
SRR (1 bit)
IDE (1 bit)
Extended ID[17:0]
(18 bits)
- (1 bit)
RTR (1 bit)
48.4.2.2.2 Local Priority enabled
If Local Priority is desired MCR[LPRIO_EN] must be asserted. In this case the Mailbox
PRIO field is included at the very left of the arbitration value (see the following table).
Table 48-115. Composition of the arbitration value when Local Priority is enabled
Format
Standard (IDE =
0)
Extended (IDE
= 1)
PRIO (3 bits)
PRIO (3 bits)
Mailbox Arbitration Value (35 bits)
Standard ID (11
bits)
RTR (1 bit)
IDE (1 bit)
- (18 bits)
Extended
ID[28:18] (11
bits)
SRR (1 bit)
IDE (1 bit)
Extended
ID[17:0] (18
bits)
- (1 bit)
RTR (1 bit)
As the PRIO field is the most significant part of the arbitration value Mailboxes with low
PRIO values have higher priority than Mailboxes with high PRIO values regardless the
rest of their arbitration values.
Note that the PRIO field is not part of the frame on the CAN bus. Its purpose is only to
affect the internal arbitration process.
48.4.2.3 Arbitration Process (continued)
Once the arbitration winner is found, its content is copied to a hidden auxiliary MB called
Tx Serial Message Buffer (Tx SMB), which has the same structure as a normal MB but is
not user accessible. This operation is called “move-out” and after it is done, write access
to the corresponding MB is blocked (if the AEN bit in MCR is asserted). The write
access is released in the following events:
• After the MB is transmitted
• FlexCAN enters in Freeze Mode or Bus Off
• FlexCAN loses the bus arbitration or there is an error during the transmission
At the first opportunity window on the CAN bus, the message on the Tx SMB is
transmitted according to the CAN protocol rules. FlexCAN transmits up to eight data
bytes, even if the DLC (Data Length Code) field value is greater than that.
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K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.