at91sam9263 ATMEL Corporation, at91sam9263 Datasheet - Page 667

• Manufacturer Part Number: at91sam9263
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

Figure 37-6. CAN Resynchronization
6249D–ATARM–20-Dec-07
CAN Bus Synchronization
Autobaud Mode
(before resynchronization)
(before resynchronization)
resynchronization
resynchronization
Nominal bit time
Nominal bit time
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 pro-
grammed value of the resynchronization jump width (t
When the magnitude of the phase error is larger than the resynchronization jump width and
The autobaud feature is enabled by setting the ABM field in the CAN_MR register. In this mode,
the CAN controller is only listening to the line without acknowledging the received messages. It
can not send any message. The errors flags are updated. The bit timing can be adjusted until no
error occurs (good configuration found). In this mode, the error counters are frozen. To go back
to the standard mode, the ABM bit must be cleared in the CAN_MR register.
Bit time with
Bit time with
• the phase error is positive, then PHASE_SEG1 is lengthened by an amount equal to the
• the phase error is negative, then PHASE_SEG2 is shortened by an amount equal to the
resynchronization jump width.
resynchronization jump width.
Received
Received
data bit
data bit
THE PHASE ERROR IS POSITIVE
(the transmitter is slower than the receiver)
THE PHASE ERROR IS NEGATIVE
(the transmitter is faster than the receiver)
SYNC_
SYNC_
SEG
SEG
PHASE_SEG2
PHASE_
Phase error
SEG2
Phase error
Phase error (max Tsjw)
PROP_SEG
PROP_SEG
SYNC_
SEG
SYNC_
SEG
PROP_SEG
PHASE_SEG1 PHASE_SEG2
PHASE_SEG1
PROP_SEG
Sample point
Nominal
after resynchronization
Phase error (max Tsjw)
AT91SAM9263 Preliminary
PHASE_SEG1
Sample point
Sample point
after resynchronization
PHASE_SEG2
PHASE_SEG1
SJW
SYNC_
PHASE_SEG2
SEG
).
Nominal
Sample point
PHASE_SEG2
SYNC_
SEG
SYNC_
SEG
SYNC_
SEG
667