Bosch, Bit timing – Rainbow Electronics CAN интерфейс User Manual
Page 31
BOSCH
ROBERT BOSCH GmbH, Postfach 50, D-7000 Stuttgart 1
Sep. 1991
Part A - page 29
SYNCHRONIZATION
HARD SYNCHRONIZATION
After a HARD SYNCHRONIZATION the internal bit time is restarted with SYNC_SEG.
Thus HARD SYNCHRONIZATION forces the edge which has caused the HARD
SYNCHRONIZATION to lie within the SYNCHRONIZATION SEGMENT of the
restarted bit time.
RESYNCHRONIZATION JUMP WIDTH
As a result of RESYNCHRONIZATION PHASE_SEG1 may be lengthened or
PHASE_SEG2 may be shortened. The amount of lengthening or shortening of the
PHASE BUFFER SEGMENTs has an upper bound given by the
RESYNCHRONIZATION JUMP WIDTH. The RESYNCHRONIZATION JUMP WIDTH
shall be programmable between 1 and min(4, PHASE_SEG1).
Clocking information may be derived from transitions from one bit value to the other.
The property that only a fixed maximum number of successive bits have the same
value provides the possibility of resynchronizing a bus unit to the bit stream during a
frame. The maximum length between two transitions which can be used for
resynchronization is 29 bit times.
PHASE ERROR of an edge
The PHASE ERROR of an edge is given by the position of the edge relative to
SYNC_SEG, measured in TIME QUANTA. The sign of PHASE ERROR is defined as
follows:
•
e = 0 if the edge lies within SYNC_SEG.
•
e > 0 if the edge lies before the SAMPLE POINT.
•
e < 0 if the edge lies after the SAMPLE POINT of the previous bit.
RESYNCHRONIZATION
The effect of a RESYNCHRONIZATION is the same as that of a HARD
SYNCHRONIZATION, when the magnitude of the PHASE ERROR of the edge which
causes the RESYNCHRONIZATION is less than or equal to the programmed value of
the RESYNCHRONIZATION JUMP WIDTH. When the magnitude of the PHASE
ERROR is larger than the RESYNCHRONIZATION JUMP WIDTH,
•
and if the PHASE ERROR is positive, then PHASE_SEG1 is lengthened by an
amount equal to the RESYNCHRONIZATION JUMP WIDTH.
•
and if the PHASE ERROR is negative, then PHASE_SEG2 is shortened by an
amount equal to the RESYNCHRONIZATION JUMP WIDTH.
Bit Timing