FlexCAN
30-11
Freescale Semiconductor
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
30.3.4
Rx Mask Registers (RXGMASK, RX14MASK, RX15MASK)
These registers are used as acceptance masks for received frame IDs. Three masks are defined: a global
mask (RXGMASK) used for Rx buffers 0–13 and two separate masks for buffers 14 (RX14MASK) and
15 (RX15MASK). The meaning of each mask bit is the following:
MI
n
bit = 0: The corresponding incoming ID bit is don’t care.
MI
n
bit = 1: The corresponding ID bit is checked against the incoming ID bit, to see if a match exists.
These masks are used for standard and extended ID formats. The value of the mask registers should not be
changed while in normal operation (only while in freeze mode), as locked frames that matched a message
buffer (MB) through a mask may be transferred into the MB (upon release) but may no longer match.
Table 30-4. TIMER Field Descriptions
Field
Description
31–16
Reserved, must be cleared.
15–0
TIMER
Free running timer. Captured at the beginning of the identifier (ID) field of any frame on the CAN bus. This captured
value is written into the TIMESTAMP entry in a message buffer after a successful reception or transmission of a
message.
Table 30-5. Mask Examples for Normal/Extended Messages
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 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
MB3
1
1
Match for Extended Format (MB3).
Rx_Msg in
2
1 1 1 1 1 1 1 1 0 0 1
0
MB2
2
2
Match for Normal Format. (MB2).
Rx_Msg in
3
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
3
3
Mismatch for MB3 because of ID0.
Rx_Msg in
4
0 1 1 1 1 1 1 1 0 0 0
0
4
Rx_Msg in
5
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
MB14
5
RX14MASK
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
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
6
Rx_Msg in
7
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
MB14
7
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60
