Datasheet

877
SAM9X35 [DATASHEET]
11055E–ATARM–10-Mar-2014
Because this number is even, we choose Tphs2 = Tphs1 (else we would choose Tphs2
= Tphs1 + Tcsc)
Tphs1 = Tphs2 = (12/2) Tcsc = 6 Tcsc
=> PHASE1 = PHASE2 = Tphs1/Tcsc - 1 = 5
The resynchronization jump width must be comprised between 1 Tcsc and the
minimum of 4 Tcsc and Tphs1. We choose its maximum value:
Tsjw = Min(4 Tcsc,Tphs1) = 4 Tcsc
=> SJW = Tsjw/Tcsc - 1 = 3
Finally: CAN_BR = 0x00053255
CAN Bus Synchronization
Two types of synchronization are distinguished: “hard synchronization” at the start of a frame and “resynchronization”
inside a frame. After a hard synchronization, the bit time is restarted with the end of the SYNC_SEG segment, regardless
of the phase error. Resynchronization causes a reduction or increase in the bit time so that the position of the sample
point is shifted with respect to the detected edge.
The effect of resynchronization is the same as that of hard synchronization when the magnitude of the phase error of the
edge causing the resynchronization is less than or equal to the programmed value of the resynchronization jump width
(t
SJW
).
When the magnitude of the phase error is larger than the resynchronization jump width and
 The phase error is positive, then PHASE_SEG1 is lengthened by an amount equal to the resynchronization jump
width.
 The phase error is negative, then PHASE_SEG2 is shortened by an amount equal to the resynchronization jump
width.
Figure 41-6. CAN Resynchronization
SYNC_
SEG
PROP_SEG PHASE_SEG1 PHASE_SEG2
SYNC_
SEG
PROP_SEG PHASE_SEG1 PHASE_SEG2
Phase error
Phase error (max Tsjw)
SYNC_
SEG
SYNC_
SEG
SYNC_
SEG
PROP_SEG PHASE_SEG1
PHASE_SEG2
SYNC_
SEG
PHASE_SEG2
SYNC_
SEG
PROP_SEG PHASE_SEG1
PHASE_
SEG2
SYNC_
SEG
PHASE_SEG2
Phase error
Nominal
Sample point
Sample point
after resynchronization
Nominal
Sample point
Sample point
after resynchronization
THE PHASE ERROR IS POSITIVE
(the transmitter is slower than the receiver)
Received
data bit
Received
data bit
Nominal bit time
(before resynchronization)
Bit time with
resynchronization
Bit time with
resynchronization
Phase error (max Tsjw)
Nominal bit time
(before resynchronization)
THE PHASE ERROR IS NEGATIVE
(the transmitter is faster than the receiver)