XC886/888CLM
Controller Area Network (MultiCAN) Controller
User’s Manual
15-8
V1.3, 2010-02
MultiCAN, V1.0
15.1.3
CAN Node Control
Each CAN node may be configured and run independently from the other CAN nodes.
Each CAN node is equipped with an individual set of SFR registers to control and to
monitor the CAN node.
Note: In the following descriptions, index “x” stands for the node number and index “n”
represents the message object number.
15.1.3.1
Bit Timing Unit
According to the ISO 11898 standard, a CAN bit time is subdivided into different
segments (
). Each segment consists of multiples of a time quantum
t
q
. The
magnitude of
t
q
is adjusted by bit fields NBTRx.BRP and NBTRx.DIV8, both controlling
the baud rate prescaler. The baud rate prescaler is driven by the module clock
f
CAN
.
Figure 15-4
CAN Bus Bit Timing Standard
The Synchronization Segment (T
Sync
) allows a phase synchronization between
transmitter and receiver time base. The Synchronization Segment length is always
one
t
q
. The Propagation Time Segment (T
Prop
) takes into account the physical
propagation delay in the transmitter output driver on the CAN bus line and in the
transceiver circuit. For a working collision detection mechanism, T
Prop
must be two times
the sum of all propagation delay quantities rounded up to a multiple of
t
q
. The phase
buffer segments 1 and 2 (T
b1
, T
b2
) before and after the signal sample point are used to
compensate for a mismatch between transmitter and receiver clock phases detected in
the synchronization segment.
The maximum number of time quanta allowed for re-synchronization is defined by bit
field NBTRx.SJW. The Propagation Time Segment and the Phase Buffer Segment 1 are
combined to parameter T
Seg1
, which is defined by the value NBTRx.TSEG1. A minimum
of 3 time quanta is requested by the ISO standard. Parameter T
Seg2
, which is defined by
the value of NBTRx.TSEG2, covers the Phase Buffer Segment 2. A minimum of 2 time
MCT04518
Sync.
Seg
T
Sync
T
Prop
T
b1
T
b2
T
Seg2
T
Seg1
1 Bit Time
Sample Point
Transmit Point
1 Time Quantum (
t
q
)
*
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