NXP Semiconductors PXN2020 - Page 902

Controller Area Network (FlexCAN)
PXN20 Microcontroller Reference Manual, Rev. 1
29-18 Freescale Semiconductor
defined: a global mask, used for Rx buffers 0–13 and 16–63, and two extra masks dedicated for buffers 14
and 15. The meaning of each mask bit is the following:
• Mask bit = 0: the corresponding incoming ID bit is “don’t care.”
• Mask bit = 1: the corresponding ID bit is checked against the incoming ID bit, to see if a match
exists.
Note that these masks are used both for standard and extended ID formats. The value of mask registers
should not be changed while in normal operation. Locked frames which had matched a MB through a mask
may be transferred into the MB (upon release) but may no longer match. Table 29-9 shows some examples
of ID masking for standard and extended message buffers.
29.3.4.4.1 Rx Global Mask (CANx_RXGMASK)
This register is provided for legacy support. On the PXN20, setting the BCC bit in CANx_MCR causes
the CANx_RXGMASK Register to have no effect on the module operation.
CANx_RXGMASK is used as acceptance mask for all Rx MBs, excluding MBs 14–15, which have
individual mask registers. When the FEN bit in CANx_MCR is set (FIFO enabled), the
Table 29-9. Mask Examples for Standard/Extended Message Buffers
Base ID
ID28.................ID18
IDE
Extended ID
ID17......................................ID0
Match
MB2 ID 1 1 1 1 1 1 1 1 0 0 0 0
MB3 ID 1 1 1 1 1 1 1 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
MB4 ID 0 0 0 0 0 0 1 1 1 1 1 0
MB5 ID 0 0 0 0 0 0 1 1 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
MB14 ID 1 1 1 1 1 1 1 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
Rx Global Mask 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 1
Rx Msg in
1
1
Match for Extended Format (MB3).
1 1 1 1 1 1 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 3
Rx Msg in
2
2
Match for Standard Format. (MB2).
1 1 1 1 1 1 1 1 0 0 1 0 2
Rx Msg in
3
3
Mismatch for MB3 because of ID0.
1 1 1 1 1 1 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0
Rx Msg in
4
4
Mismatch for MB2 because of ID28.
0 1 1 1 1 1 1 1 0 0 0 0
Rx Msg in
5
5
Mismatch for MB3 because of ID28, Match for MB14 (uses CANx_RX14MASK).
0 1 1 1 1 1 1 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 14
Rx 14 Mask 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0
Rx Msg in
6
6
Mismatch for MB14 because of ID27 (uses CANx_RX14MASK).
1 0 1 1 1 1 1 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
Rx Msg in
7
7
Match for MB14 (uses CANx_RX14MASK).
0 1 1 1 1 1 1 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 14