CAN Registers
810
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Controller Area Network (CAN) Module
11.4.4 CANBIT Register (Offset = 0xC) [reset = 0x2301]
CAN Bit Timing (CANBIT)
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
for more information.
CANBIT is shown in
and described in
Return to
Figure 11-8. CANBIT Register
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
RESERVED
R-0x0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
RESE
RVED
TSEG2
TSEG1
SJW
BRP
R-0x0
R/W-0x2
R/W-0x3
R/W-0x0
R/W-0x1
Table 11-11. CANBIT Register Field Descriptions
Bit
Field
Type
Reset
Description
31-15
RESERVED
R
0x0
14-12
TSEG2
R/W
0x2
Time Segment after Sample Point.
0x00 to 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
). The bit time
quanta is defined by the BRP field.
11-8
TSEG1
R/W
0x3
Time Segment Before Sample Point.
0x00 to 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
). The bit time
quanta is defined by the BRP field.
7-6
SJW
R/W
0x0
(Re)Synchronization Jump Width.
0x00 to 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.
5-0
BRP
R/W
0x1
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 to 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.