Datasheet

661
SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
Figure 33-4. Partition of the CAN Bit Time
 SYNC SEG: SYNChronization Segment
This part of the bit time is used to synchronize the various nodes on the bus. An edge is expected to lie
within this segment. It is one TQ long.
 PROP SEG: PROPagation Segment
This part of the bit time is used to compensate for the physical delay times within the network. It is twice the
sum of the signal’s propagation time on the bus line, the input comparator delay, and the output driver delay.
It is programmable to be 1,2,..., 8 TQ long.
This parameter is defined in the PROPAG field of the ”CAN Baudrate Register”.
 PHASE SEG1, PHASE SEG2: PHASE Segment 1 and 2
The Phase-Buffer-Segments are used to compensate for edge phase errors. These segments can be
lengthened (PHASE SEG1) or shortened (PHASE SEG2) by resynchronization.
Phase Segment 1 is programmable to be 1, 2, ..., 8 TQ long.
Phase Segment 2 length has to be at least as long as the Information Processing Time (IPT) and may not be
more than the length of Phase Segment 1.
These parameters are defined in the PHASE1 and PHASE2 fields of the ”CAN Baudrate Register”.
 TIME QUANTUM
The TIME QUANTUM (TQ) is a fixed unit of time derived from the peripheral clock period. The total number
of TIME QUANTA in a bit time is programmable from 8 to 25.
 INFORMATION PROCESSING TIME
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 two 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.
 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 four TQ.
If the SMP field in the CAN_BR is set, then the incoming bit stream is sampled three times with a period of half a
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).
SYNC_SEG
PROP_SEG
PHASE_SEG1
PHASE_SEG2
NOMINAL BIT TIME
Sample Point