538
/
838
Nations Technologies Inc.
Tel
:
+86-755-86309900
:
Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
8
32 bit mask mode
9
10
16 bit mask mode
10/11
12
32 bit list mode
12/13
Filter priority rule
According to different configurations of filters, it is possible that a message identifier can be filtered by multiple
filters; In this case, the filter matching serial number stored in the receiving mailbox is first determined according to
bit width,32-bit-wide filters have higher priority than 16-bit-wide filters. For filters with the same bit width, then the
identifier list mode takes precedence over the mask mode. If filters have the same bit width and mode, the priority is
determined by the filter group number, and the filter group with lower number has the higher priority.Within a filter
group,the lower the filter number,the higher the priority.
Figure 20-10 Examples of filter mechanisms
Figure 20-10 illustrates the filter rules of CAN. When receiving a message, its identifier is first compared with the
filter configured in identifier list mode. If there is a match, the message will be stored in the associated FIFO, and the
serial number of the matched filter will be stored in the filter matching serial number.
If there is no match, the message identifier is then compared with the filter configured in the mask mode. And the
hardware will automatically discard the message without software intervention if the message identifier does not
match any identifier in the filter.
20.4.6
Message storage
A mailbox contains all information related to a message: identifier, data, control, status and time stamp information.
Mailbox is the interface between software and hardware to transfer messages.
Send mailbox
Message should be written into an empty sending mailbox by software before enable the sending request. You can
query the sending status through the CAN_TSTS register.
Received Message
Filter
FIFO0_1
match?
Filter
FIFO0_2
match?
Filter
FIFO1_0
match?
Filter
FIFO1_1
match?
Configure:
Discard Message
Receive FIFO0
Mailbox 1
Mailbox 2
Mailbox 0
Receive FIFO1
Mailbox 1
Mailbox 2
Mailbox 0
Filter
FIFO0_2
match?
N
N
N
N
N
Y
Y
Y
Y