Chapter 16 Freescale’s Scalable Controller Area Network (S12MSCANV3)
MC9S12XE-Family Reference Manual Rev. 1.19
Freescale Semiconductor
613
16.3.2.4
MSCAN Bus Timing Register 1 (CANBTR1)
The CANBTR1 register configures various CAN bus timing parameters of the MSCAN module.
Read: Anytime
Write: Anytime in initialization mode (INITRQ = 1 and INITAK = 1)
1
1
4 Tq clock cycles
Table 16-6. Baud Rate Prescaler
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
Prescaler value (P)
0
0
0
0
0
0
1
0
0
0
0
0
1
2
0
0
0
0
1
0
3
0
0
0
0
1
1
4
:
:
:
:
:
:
:
1
1
1
1
1
1
64
Module Base + 0x0003
7
6
5
4
3
2
1
0
R
SAMP
TSEG22
TSEG21
TSEG20
TSEG13
TSEG12
TSEG11
TSEG10
W
Reset:
0
0
0
0
0
0
0
0
Figure 16-7. MSCAN Bus Timing Register 1 (CANBTR1)
Table 16-7. CANBTR1 Register Field Descriptions
Field
Description
7
SAMP
Sampling
— This bit determines the number of CAN bus samples taken per bit time.
0 One sample per bit.
1 Three samples per bit
(1)
.
If SAMP = 0, the resulting bit value is equal to the value of the single bit positioned at the sample point. If
SAMP = 1, the resulting bit value is determined by using majority rule on the three total samples. For higher bit
rates, it is recommended that only one sample is taken per bit time (SAMP = 0).
1. In this case, PHASE_SEG1 must be at least 2 time quanta (Tq).
6:4
TSEG2[2:0]
Time Segment 2
— Time segments within the bit time fix the number of clock cycles per bit time and the location
of the sample point (see
). Time segment 2 (TSEG2) values are programmable as shown in
.
3:0
TSEG1[3:0]
Time Segment 1
— Time segments within the bit time fix the number of clock cycles per bit time and the location
of the sample point (see
). Time segment 1 (TSEG1) values are programmable as shown in
.
Table 16-5. Synchronization Jump Width (continued)
SJW1
SJW0
Synchronization Jump Width
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:
S12XE
products
in
208
MAPBGA
packages