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M0A21/M0A23 Series
May 06, 2022
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Rev 1.02
M0
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ANUAL
When the phase error of the edge, which causes Re-synchronization is negative, Phase_Seg2 is
shortened. If the magnitude of the phase error is less than SJW, Phase_Seg2 is shortened by the
magnitude of the phase error, else it is shortened by SJW.
When the magnitude of the phase error of the edge is less than or equal to the programmed value of
SJW, the results of Hard Synchronization and Re-synchronization are the same. If the magnitude of the
phase error is larger than SJW, the Re-synchronization cannot compensate the phase error completely,
an error (phase error - SJW) remains.
Only one synchronization may be done between two Sample Points. The Synchronizations maintain a
minimum distance between edges and Sample Points, giving the bus level time to stabilize and filtering
out spikes that are shorter than (Pr Phase_Seg1).
Apart from noise spikes
, most synchronizations are caused by arbitration. All nodes synchronize “hard”
on the edge transmitted by the “leading” transceiver that started transmitting first, but due to propagation
delay time, they cannot become ideally synchronized. The “leading” transmitter does not necessarily
win the arbitration, therefore the receivers have to synchronize themselves to different transmitters that
subsequently “take the lead” and that are differently synchronized to the previously “leading” transmitter.
The same happens at the acknowledge field, where the transmitter and some of the receivers will have
to synchronize to that receiver that “takes the lead” in the transmission of the dominant acknowledge
bit.
Synchronizations after the end of the arbitration will be caused by oscillator tolerance, when the
differences in the oscillator’s clock periods of transmitter and receivers sum up during the time between
synchronizations (at most ten bits). These summarized differences may not be longer than the SJW,
limiting
the oscillator’s tolerance range.
The examples in Figure 6.16-9 show how the Phase Buffer Segments are used to compensate for phase
errors. There are three drawings of each two consecutive bit timings. The upper drawing shows the
synchronization on a “late” edge, the lower drawing shows the synchronization on an “early” edge, and
the middle drawing is the reference without synchronization.
Rx-Input
recessive
dominant
Sync_Seg
Prop_Seg
Phase_Seg
Prop_Seg
Sample-Point
Sample-Point
Sample-Point
Sample-Point
Sample-Point
Sample-Point
recessive
dominant
Rx-Input
“early Edge
Figure 6.16-9
Synchronization on “late” and “early” Edges
In the first example an edge from recessive to dominant occurs at the end of Prop_Seg. The edge is
“late” since it occurs after the Sync_Seg. Reacting to the “late” edge, Phase_Seg1 is lengthened so that
the distance from the edge to the Sample Point is the same as it would have been from the Sync_Seg
to the Sample Point if no edge had occurred. The phase error of this “late” edge is less than SJW, so it
is fully compensated and the edge from dominant to recessive at the end of the bit, which is one nominal