MOTOROLA
Chapter 16. CAN 2.0B Controller Module
16-33
Programming Model
16.7.9
Receive Global Mask Registers (RXGMSKHI,
RXGMSKLO)
Table 16-19. TIMER Bit Descriptions
Bits
Name
Description
0:15
TIMER
The free running timer counter can be read and written by the CPU. The timer starts from
zero after reset, counts linearly to 0xFFFF, and wraps around.
The timer is clocked by the TouCAN bit-clock. During a message, it increments by one for
each bit that is received or transmitted. When there is no message on the bus, it increments
at the nominal bit rate.
The timer value is captured at the beginning of the identifier field of any frame on the CAN
bus. The captured value is written into the “time stamp” entry in a message buffer after a
successful reception or transmission of a message.
MSB
0123456
789
10
11
12
13
14
15
Field MID
28
MID
27
MID
26
MID
25
MID
24
MID
23
MID
22
MID
21
MID
20
MID
19
MID
18
01
MID
17
MID
16
MID
15
SRESET
11111111111
0
1
Addr
0x30 7090 (RxGMSKHI_A); 0x30 7490 (RxGMSKHI_B); 0x30 7890 (RxGMSKHI_C);
0x30 7092 (RxGMSKLO_A); 0x30 7492 (RxGMSKLO_B); 0x30 7892 (RxGMSKLO_C)
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
LSB
31
Field MID
14
MID
13
MID
12
MID
11
MID
10
MID
9
MID
8
MID
7
MID
6
MID
5
MID
4
MID
3
MID
2
MID
1
MID
0
SRESET
11111111111
1
0
Figure 16-16. Receive Global Mask Register: High (RXGMSKHI), Low (RXGMSKLO)
Table 16-20. RXGMSKHI, RXGMSKLO Bit Descriptions
Bits
Name
Description
0:31
MIDx
The receive global mask registers use four bytes. The mask bits are applied to all
receive-identifiers, excluding receive-buffers 14 and 15, which have their own specific mask
registers.
Base ID mask bits MID[28:18] are used to mask standard or extended format frames.
Extended ID bits MID[17:0] are used to mask only extended format frames.
The RTR/SRR bit of a received frame is never compared to the corresponding bit in the
message buffer ID field. However, remote request frames (RTR = 1) once received, are never
stored into the message buffers. RTR mask bit locations in the mask registers (bits 11 and
31) are always zero, regardless of any write to these bits.
The IDE bit of a received frame is always compared to determine if the message contains a
standard or extended identifier. Its location in the mask registers (bit 12) is always one,
regardless of any write to this bit.