Datasheet

Freescale’s Scalable Controller Area Network (S12MSCANV3)
S12XS Family Reference Manual, Rev. 1.13
306 Freescale Semiconductor
11.3.2.4 MSCAN Bus Timing Register 1 (CANBTR1)
The CANBTR1 register configures various CAN bus timing parameters of the MSCAN module.
Table 11-7. Baud Rate Prescaler
BRP5 BRP4 BRP3 BRP2 BRP1 BRP0 Prescaler value (P)
000000 1
000001 2
000010 3
000011 4
:::::: :
111111 64
Module Base + 0x0003 Access: User read/write
(1)
1. Read: Anytime
Write: Anytime in initialization mode (INITRQ = 1 and INITAK = 1)
76543210
R
SAMP TSEG22 TSEG21 TSEG20 TSEG13 TSEG12 TSEG11 TSEG10
W
Reset: 00000000
Figure 11-7. MSCAN Bus Timing Register 1 (CANBTR1)
Table 11-8. 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
(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 Figure 11-44). Time segment 2 (TSEG2) values are programmable as shown in
Table 11-9.
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 Figure 11-44). Time segment 1 (TSEG1) values are programmable as shown in
Table 11-10.