RM0090: Reference manual - STMicroelectronics

Controller area network (bxCAN) RM0090
Figure 231. Filter bank scale configuration - register organization
FSCx = 1
FSCx = 0
Filter Bank Scale
Config. Bits1 FBMx = 0
FBMx = 1
FBMx = 0
FBMx = 1
Filter Bank Mode 2
One 32-Bit Filter - Identifier Mask
ID
Mask
Mapping
Two 16-Bit Filters - Identifier Mask
ID
Mask
ID
Mask
Mapping
Filter match index
CAN_FxR1[31:24]
CAN_FxR2[31:24]
STID[10:3] STID[2:0] EXID[17:13]
EXID[12:5]
Two 32-Bit Filters - Identifier List
ID
ID
Mapping
CAN_FxR1[31:24] CAN_FxR1[23:16] CAN_FxR1[15:8] CAN_FxR1[7:0]
CAN_FxR2[31:24] CAN_FxR2[23:16] CAN_FxR2[15:8] CAN_FxR2[7:0]
STID[10:3] STID[2:0] EXID[17:13]
EXID[12:5]
EXID[4:0] IDE RTR 0
CAN_FxR1[15:8]
CAN_FxR1[31:24]
STID[10:3]
Four 16-Bit Filters - Identifier List
ID
ID
ID
ID
Mapping
CAN_FxR2[15:8]
CAN_FxR2[31:24]
CAN_FxR1[15:8]
CAN_FxR1[31:24]
CAN_FxR2[15:8]
CAN_FxR2[31:24]
STID[10:3]
CAN_FxR1[7:0]
CAN_FxR1[23:16]
STID[2:0] RTR IDE EXID[17:15]
STID[2:0] RTR IDE EXID[17:15]
Once a message has been received in the FIFO it is available to the application. Typically,
application data is copied into SRAM locations. To copy the data to the right location the
application has to identify the data by means of the identifier. To avoid this, and to ease the
access to the SRAM locations, the CAN controller provides a Filter Match Index.
This index is stored in the mailbox together with the message according to the filter priority
rules. Thus each received message has its associated filter match index.
The Filter Match index can be used in two ways:
● Compare the Filter Match index with a list of expected values.
● Use the Filter Match Index as an index on an array to access the data destination
location.
For nonmasked filters, the software no longer has to compare the identifier.
If the filter is masked the software reduces the comparison to the masked bits only.
The index value of the filter number does not take into account the activation state of the
filter banks. In addition, two independent numbering schemes are used, one for each FIFO.
Refer to Figure 232 for an example.
671/1416 Doc ID 018909 Rev 3
CAN_FxR1[23:16] CAN_FxR1[15:8] CAN_FxR1[7:0]
CAN_FxR2[23:16] CAN_FxR2[15:8] CAN_FxR2[7:0]
CAN_FxR2[7:0]
CAN_FxR2[23:16]
CAN_FxR1[7:0]
CAN_FxR1[23:16]
CAN_FxR2[7:0]
CAN_FxR2[23:16]
EXID[4:0] IDE RTR 0
Filter
Num.
n
n+1
n
n+1
n+2
n+3
x = filter bank number
ID=Identifier
1 These bits are located in the CAN_FS1R register
2
These bits are located in the CAN_FM1R register
n
n
n+1