Atmel Evaluation Kit AT91SAM9X25-EK AT91SAM9X25-EK Data Sheet
Product codes
AT91SAM9X25-EK
904
SAM9X25 [DATASHEET]
11054E–ATARM–10-Mar-2014
The Information Processing Time (IPT) is the time required for the logic to determine the bit level of a sampled bit. The
IPT begins at the sample point, is measured in TQ and is fixed at 2 TQ for the Atmel CAN. Since Phase Segment 2 also
begins at the sample point and is the last segment in the bit time, PHASE SEG2 shall not be less than the IPT.
IPT begins at the sample point, is measured in TQ and is fixed at 2 TQ for the Atmel CAN. Since Phase Segment 2 also
begins at the sample point and is the last segment in the bit time, PHASE SEG2 shall not be less than the IPT.
SAMPLE POINT:
The SAMPLE POINT is the point in time at which the bus level is read and interpreted as the value of that respective bit.
Its location is at the end of PHASE_SEG1.
Its location is at the end of PHASE_SEG1.
SJW: ReSynchronization Jump Width.
The ReSynchronization Jump Width defines the limit to the amount of lengthening or shortening of the Phase Segments.
SJW is programmable to be the minimum of PHASE SEG1 and 4 TQ.
If the SMP field in the CAN_BR register is set, then the incoming bit stream is sampled three times with a period of half a
CAN clock period, centered on sample point.
CAN clock period, centered on sample point.
In the CAN controller, the length of a bit on the CAN bus is determined by the parameters (BRP, PROPAG, PHASE1 and
PHASE2).
PHASE2).
The time quantum is calculated as follows:
Note: The BRP field must be within the range [1, 0x7F], i.e., BRP = 0 is not authorized.
To compensate for phase shifts between clock oscillators of different controllers on the bus, the CAN controller must
resynchronize on any relevant signal edge of the current transmission. The resynchronization shortens or lengthens the
bit time so that the position of the sample point is shifted with regard to the detected edge. The resynchronization jump
width (SJW) defines the maximum of time by which a bit period may be shortened or lengthened by resynchronization.
resynchronize on any relevant signal edge of the current transmission. The resynchronization shortens or lengthens the
bit time so that the position of the sample point is shifted with regard to the detected edge. The resynchronization jump
width (SJW) defines the maximum of time by which a bit period may be shortened or lengthened by resynchronization.
Figure 41-5. CAN Bit Timing
t
BIT
t
CSC
t
PRS
t
PHS1
t
PHS2
+
+
+
=
t
CSC
BRP 1
+
(
) MCK
⁄
=
t
PRS
t
CSC
PROPAG 1
+
(
)
×
=
t
PHS1
t
CSC
PHASE1 1
+
(
)
×
=
t
PHS2
t
CSC
PHASE2 1
+
(
)
×
=
t
SJW
t
CSC
SJW 1
+
(
)
×
=
SYNC_
SEG
PROP_SEG
PHASE_SEG1
PHASE_SEG2
NOMINAL BIT TIME
Sample Point
Transmission Point
MCK
CAN Clock
t
CSC
t
PRS
t
PHS1
t
PHS2