Rainbow Electronics ATmega64M1 - Manual (Page 167)

167
8209A–AVR–08/09
ATmega16M1/32M1/64M1
Figure 20-3. CAN Bit Construction
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.
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
Sample Point
Transmission Point
(producer)
CAN Frame
(producer)