Information

Whenever CAN bit is used as a measure of duration (e.g. MCR[FRZACK] and
MCR[LPMACK]), the number of peripheral clocks in one CAN bit can be calculated as:
NCCP
=
f
CANCLK
f
SYS
x [1 + (PSEG1 + 1) + (PSEG2 + 1) + (PROPSEG + 1)] x (PRESDIV + 1)
where:
• NCCP is the number of peripheral clocks in one CAN bit;
• f
CANCLK
is the Protocol Engine (PE) Clock (see Figure "CAN Engine Clocking
Scheme"), in Hz;
• f
SYS
is the frequency of operation of the system (CHI) clock, in Hz;
• PSEG1 is the value in CTRL1[PSEG1] field;
• PSEG2 is the value in CTRL1[PSEG2] field;
• PROPSEG is the value in CTRL1[PROPSEG] field;
• PRESDIV is the value in CTRL1[PRESDIV] field.
For example, 180 CAN bits = 180 x NCCP peripheral clock periods.
Table 42-118. Time Segment Syntax
Syntax Description
SYNC_SEG System expects transitions to occur on the bus during this period.
Transmit Point A node in transmit mode transfers a new value to the CAN bus at this point.
Sample Point A node samples the bus at this point. If the three samples per bit option is selected, then this point
marks the position of the third sample.
The following table gives an overview of the CAN compliant segment settings and the
related parameter values.
Table 42-119. CAN Standard Compliant Bit Time Segment Settings
Time Segment 1 Time Segment 2 Re-synchronization Jump Width
5 .. 10 2 1 .. 2
4 .. 11 3 1 .. 3
5 .. 12 4 1 .. 4
6 .. 13 5 1 .. 4
7 .. 14 6 1 .. 4
8 .. 15 7 1 .. 4
9 .. 16 8 1 .. 4
Chapter 42 CAN (FlexCAN)
K10 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc. 1149