Rainbow Electronics CAN интерфейс - Manual (Page 70)

BOSCH
ROBERT BOSCH GmbH, Postfach 300240, D-7000 Stuttgart 30
Sep. 1991
Part B - page 68
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.
SYNCHRONIZATION RULES
HARD SYNCHRONIZATION and RESYNCHRONIZATION are the two forms of
SYNCHRONIZATION. They obey the following rules:
1. Only one SYNCHRONIZATION within one bit time is allowed.
2. An edge will be used for SYNCHRONIZATION only if the value detected at the
previous SAMPLE POINT (previous read bus value) differs from the bus value
immediately after the edge.
3. HARD SYNCHRONIZATION is performed whenever there is a ’recessive’ to
’dominant’ edge during BUS IDLE.
4. All other ’recessive’ to ’dominant’ edges fulfilling the rules 1 and 2 will be used for
RESYNCHRONIZATION with the exception that a node transmitting a dominant bit
will not perform a RESYNCHRONIZATION as a result of a ’recessive’ to ’dominant’
edge with a positive PHASE ERROR, if only ’recessive’ to ’dominant’ edges are
used for resynchronization.
Bit Timing