LM3S9781_15 Datasheet, PDF (878/1271 Pages) Texas Instruments – Stellaris LM3S9781 Microcontroller

Controller Area Network (CAN) Module
Register 4: CAN Bit Timing (CANBIT), offset 0x00C
This register is used to program the bit width and bit quantum. Values are programmed to the system
clock frequency. This register is write-enabled by setting the CCE and INIT bits in the CANCTL
register. See “Bit Time and Bit Rate” on page 864 for more information.
CAN Bit Timing (CANBIT)
CAN0 base: 0x4004.0000
CAN1 base: 0x4004.1000
CAN2 base: 0x4004.2000
Offset 0x00C
Type R/W, reset 0x0000.2301
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
reserved
Type RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
reserved
TSEG2
TSEG1
SJW
BRP
Type RO
Reset
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
1
0
0
0
1
1
0
0
0
0
0
0
0
1
Bit/Field
31:15
14:12
11:8
7:6
5:0
Name
reserved
TSEG2
TSEG1
SJW
BRP
Type
RO
R/W
R/W
R/W
R/W
Reset
0x0000
0x2
0x3
0x0
0x1
Description
Software should not rely on the value of a reserved bit. To provide
compatibility with future products, the value of a reserved bit should be
preserved across a read-modify-write operation.
Time Segment after Sample Point
0x00-0x07: The actual interpretation by the hardware of this value is
such that one more than the value programmed here is used.
So, for example, the reset value of 0x2 means that 3 (2+1) bit time
quanta are defined for Phase2 (see Figure 17-4 on page 865). The bit
time quanta is defined by the BRP field.
Time Segment Before Sample Point
0x00-0x0F: The actual interpretation by the hardware of this value is
such that one more than the value programmed here is used.
So, for example, the reset value of 0x3 means that 4 (3+1) bit time
quanta are defined for Phase1 (see Figure 17-4 on page 865). The bit
time quanta is defined by the BRP field.
(Re)Synchronization Jump Width
0x00-0x03: The actual interpretation by the hardware of this value is
such that one more than the value programmed here is used.
During the start of frame (SOF), if the CAN controller detects a phase
error (misalignment), it can adjust the length of TSEG2 or TSEG1 by the
value in SJW. So the reset value of 0 adjusts the length by 1 bit time
quanta.
Baud Rate Prescaler
The value by which the oscillator frequency is divided for generating the
bit time quanta. The bit time is built up from a multiple of this quantum.
0x00-0x03F: The actual interpretation by the hardware of this value is
such that one more than the value programmed here is used.
BRP defines the number of CAN clock periods that make up 1 bit time
quanta, so the reset value is 2 bit time quanta (1+1).
The CANBRPE register can be used to further divide the bit time.
878
July 03, 2014
Texas Instruments-Production Data