© 2004 Microchip Technology Inc. DS70070B-page 23-63
Section 23. CAN
CAN Module
23
23.9.6.2 Re-synchronization
As a result of re-synchronization phase segment 1 may be lengthened or phase segment 2 may
be shortened. The amount of lengthening or shortening of the phase buffer segment, specified
by the SJW<1:0> bits (CiCFG1<7:6>), has an upper bound given by the re-synchronization jump
width bits. The value of the synchronization jump width will be added to phase segment 1 or
subtracted from phase segment 2. The re-synchronization jump width is programmable between
1T
Q and 4 TQ.
Clocking information will only be derived from transitions of recessive to dominant bus states.
The property that only a fixed maximum number of successive bits have the same value ensures
resynchronizing a bus unit to the bit stream during a frame (e.g., bit-stuffing).
The phase error of an edge is given by the position of the edge relative to Synchronous Segment,
measured in Time Quanta. The phase error is defined in magnitude of T
Q as follows:
• e = 0 if the edge lies within the Synchronous Segment.
• e > 0 if the edge lies before the Sample Point.
• e < 0 if the edge lies after the Sample Point of the previous bit.
If the magnitude of the phase error is less than or equal to the programmed value of the
re-synchronization jump width, the effect of a re-synchronization is the same as that of a hard
synchronization.
If the magnitude of the phase error is larger than the re-synchronization jump width, and if the
phase error is positive, then phase segment 1 is lengthened by an amount equal to the
re-synchronization jump width.
If the magnitude of the phase error is larger than the re-synchronization jump width, and if the
phase error is negative, then phase segment 2 is shortened by an amount equal to the
re-synchronization jump width.
Figure 23-21: Lengthening a Bit Period
Figure 23-22: Shortening a Bit Period
Input Signal
Sync
Propagation
Segment
Phase
Segment 1
Phase
Segment 2
≤ sjw
Sample
Nominal
Actual Bit
Length
Bit Length
Point
TQ
Input Signal
Sync
Propagation
Segment
Phase
Segment 1
Phase
Segment 2
≤
sjw
Sample
Actual
Nominal
Bit Length
T
Q
Point
Bit Length
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