Datasheet

Figure 20-3. CAN bit construction
Time quantum
(producer)
Nominal CAN Bit Time
Segments
(producer)
SYNC_SEG
PROP_SEG PHASE_SEG_1 PHASE_SEG_2
propagation
delay
Segments
(consumer)
SYNC_SEG
PROP_SEG PHASE_SEG_1 PHASE_SEG_2
Transmission point
(producer)
CAN frame
(producer)
20.3.3.2. Synchronization segment
The first segment is used to synchronize the various bus nodes.
On transmission, at the start of this segment, the current bit level is output. If there is a bit state change
between the previous bit and the current bit, then the bus state change is expected to occur within this
segment by the receiving nodes.
20.3.3.3. Propagation time segment
This segment is used to compensate for signal delays across the network.
This is necessary to compensate for signal propagation delays on the bus line and through the
transceivers of the bus nodes.
20.3.3.4. Phase Segment 1
Phase Segment 1 is used to compensate for edge phase errors.
This segment may be lengthened during re-synchronization.
20.3.3.5. Sample point
The sample point is the point of time at which the bus level is read and interpreted as the value of the
respective bit. Its location is at the end of Phase Segment 1 (between the two Phase Segments).
20.3.3.6. Phase Segment 2
This segment is also used to compensate for edge phase errors.
This segment may be shortened during re-synchronization, but the 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.
20.3.3.7. Information processing time
It 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 2TQ for the Atmel CAN. Since
Phase Segment 2 also begins at the sample point and is the last segment in the bit time, PS2 minimum
shall not be less than the IPT.
20.3.3.8. Bit lengthening
As a result of resynchronization, Phase Segment 1 may be lengthened or Phase Segment 2 may be
shortened to compensate for oscillator tolerances. If, for example, the transmitter oscillator is slower than
the receiver oscillator, the next falling edge used for resynchronization may be delayed. So Phase
Segment 1 is lengthened in order to adjust the sample point and the end of the bit time.
Atmel ATmega16M1/32M1/64M1 [DATASHEET]
Atmel-8209F-ATmega16M1/32M1/64M1_Datasheet_Complete-10/2016
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