MC68F375
CAN 2.0B CONTROLLER MODULE
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
7-30
7.8.8 Receive Global Mask Registers
7.8.9 Receive Buffer 14 Mask Registers
RX14MSKHI — Receive Buffer 14 Mask Register High
0xYF F094
RX14MSKLO — Receive Buffer 14 Mask Register Low
0xYF F096
The receive buffer 14 mask registers have the same structure as the receive global
mask registers and are used to mask buffer 14.
Table 7-19 TIMER Bit Settings
Bit(s)
Name
Description
15:0
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 suc-
cessful reception or transmission of a message.
RXGMSKHI — Receive Global Mask Register High
0xYF F090
RXGMSKLO — Receive Global Mask Register Low
0xYF F092
MSB
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
LSB
16
MID28 MID27 MID26 MID25 MID24 MID23 MID22 MID21 MID20 MID19
MID18
0
1
MID17 MID16 MID15
RESET:
1
0
1
MSB
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
LSB
0
MID14 MID13 MID12 MID11 MID10
MID9
MID8
MID7
MID6
MID5
MID4
MID3
MID2
MID1
MID0
0
RESET:
1
0
Table 7-20 RXGMSKHI, RXGMSKLO Bit Settings
Bit(s)
Name
Description
31:0
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 mes-
sage 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 20 and
0) 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 19) is always one,
regardless of any write to this bit.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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