ST SPC560P34 - Figure 277. Segments Within the Bit Time

RM0046 FlexCAN
Doc ID 16912 Rev 5 569/936
The PRESDIV field controls a prescaler that generates the Serial Clock (Sclock), whose
period defines the ‘time quantum’ used to compose the CAN waveform. A time quantum is
the atomic unit of time handled by the CAN engine.
Equation 32
A bit time is subdivided into three segments
(c)
(reference Figure 277 and Table 2 86):
● SYNC_SEG: This segment has a fixed length of one time quantum. Signal edges are
expected to happen within this section.
● Time Segment 1: This segment includes the Propagation Segment and the Phase
Segment 1 of the CAN standard. It can be programmed by setting the PROPSEG and
the PSEG1 fields of the CTRL Register so that their sum (plus 2) is in the range of 4 to
16 time quanta.
● Time Segment 2: This segment represents the Phase Segment 2 of the CAN standard.
It can be programmed by setting the PSEG2 field of the CTRL Register (plus 1) to be 2
to 8 time quanta long.
Equation 33
Figure 277. Segments within the bit time
c. For further explanation of the underlying concepts please refer to ISO/DIS 11519–1, Section 10.3. Reference
also the Bosch CAN 2.0A/B protocol specification dated September 1991 for bit timing.
f
Tq
f
CANCLK
Prescaler ValueÞ
--------------------------------------------------------=
Bit Rate
f
Tq
number of Time QuantaÞÞ Þ
-----------------------------------------------------------------------------------------=Þ
SYNC_SEG
Time Segment 1 Time Segment 2
1 4 ... 16 2 ... 8
8 ... 25 Time Quanta
= 1 Bit Time
NRZ Signal
Sample Point
(single or triple sampling)
(PROP_SEG + PSEG1 + 2) (PSEG2 + 1)
Transmit Point