Freescale Semiconductor Tower System Eval Kit for MC9S12GN32 TWR-S12GN32-KIT TWR-S12GN32-KIT Hoja De Datos
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TWR-S12GN32-KIT
Freescale’s Scalable Controller Area Network (S12MSCANV3)
MC9S12G Family Reference Manual, Rev.1.23
Freescale Semiconductor
595
18.3.2.4
MSCAN Bus Timing Register 1 (CANBTR1)
The CANBTR1 register configures various CAN bus timing parameters of the MSCAN module.
Table 18-7. 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
Access: User read/write
1
1
Read: Anytime
Write: Anytime in initialization mode (INITRQ = 1 and INITAK = 1)
Write: Anytime in initialization mode (INITRQ = 1 and INITAK = 1)
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 18-7. MSCAN Bus Timing Register 1 (CANBTR1)
Table 18-8. 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
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).
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
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
of the sample point (see
). Time segment 1 (TSEG1) values are programmable as shown in
.