P912XDP512F0MPVR datasheet(429/1348 Pages) FREESCALE

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Chapter 10 Freescale’s Scalable Controller Area Network (S12MSCANV3)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

429

10.3.2.4

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)

Table 10-5. Baud Rate Prescaler

BRP5

BRP4

BRP3

BRP2

BRP1

BRP0

Prescaler value (P)

000000

000001

000010

000011

::::::

111111

76543210

SAMP

TSEG22

TSEG21

TSEG20

TSEG13

TSEG12

TSEG11

TSEG10

Reset:

00000000

Figure 10-7. MSCAN Bus Timing Register 1 (CANBTR1)

Table 10-6. CANBTR1 Register Field Descriptions

Field

Description

SAMP

Sampling — This bit determines the number of CAN bus samples taken per bit time.

0 One sample per bit.

1 Three samples per bit1.

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 10-44). Time segment 2 (TSEG2) values are programmable as shown in

Table 10-7.

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 10-44). Time segment 1 (TSEG1) values are programmable as shown in

Table 10-8.

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