MCBSTM32EXL Keil, MCBSTM32EXL Datasheet - Page 556

• Manufacturer Part Number: MCBSTM32EXL
• Description: BOARD EVALUATION FOR STM32F103ZE
• Manufacturer: Keil

Specifications of MCBSTM32EXL

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Controller area network (bxCAN)
22.7.5
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Figure 202. Filtering mechanism - example
The example above shows the filtering principle of the bxCAN. On reception of a message,
the identifier is compared first with the filters configured in identifier list mode. If there is a
match, the message is stored in the associated FIFO and the index of the matching filter is
stored in the Filter Match Index. As shown in the example, the identifier matches with
Identifier #2 thus the message content and FMI 2 is stored in the FIFO.
If there is no match, the incoming identifier is then compared with the filters configured in
mask mode.
If the identifier does not match any of the identifiers configured in the filters, the message is
discarded by hardware without disturbing the software.
Message storage
The interface between the software and the hardware for the CAN messages is
implemented by means of mailboxes. A mailbox contains all information related to a
message; identifier, data, control, status and time stamp information.
Transmit mailbox
The software sets up the message to be transmitted in an empty transmit mailbox. The
status of the transmission is indicated by hardware in the CAN_TSR register.
Example of 3 filter banks in 32-bit Unidentified List mode and
Filter bank
Num
0
2
3
1
4
the remaining in 32-bit Identifier Mask mode
Message Discarded
Identifier
Identifier
Mask
Identifier
Identifier
Identifier
Identifier
Mask
No Match
Found
Identifier
2
3
5
0
1
4
Doc ID 13902 Rev 9
Ctrl
Message Received
Identifier #4 Match
Data
Receive FIFO
Message
Stored
FMI
Filter number stored in the
Filter Match Index field
within the CAN_RDTxR
register
RM0008