TC1796
Peripheral Units (Vol. 2 of 2)
Controller Area Network (MultiCAN) Controller
User’s Manual
22-8
V2.0, 2007-07
MultiCAN, V2.0
22.1.3
The Nominal Bit Time
One bit cell (this means one high or low pulse of the NRZ code) is composed by four
segments. Each segment is an integer multiple of Time Quanta
t
Q
. The Time Quanta is
the smallest discrete timing resolution used by a CAN node. The nominal bit time
definition with its segments is shown in
.
Figure 22-4 Partition of Nominal Bit Time
The Synchronization Segment (SYNC_SEG) is used to synchronize the various bus
nodes. If there is a bit state change between the previous bit and the current bit, the bus
state change is expected to occur within this segment. The length of this segment is
always 1
t
Q
.
The Propagation Segment (PROP_SEG) is used to compensate for signal delays across
the network. These delays are caused by signal propagation delay on the bus line and
through the electronic interface circuits of the bus nodes.
The Phase Segments 1 and 2 (PHASE_SEG1, PHASE_SEG2) are used to compensate
for edge phase errors. These segments can be lengthened or shortened by re-
synchronization. PHASE_SEG2 is reserved for calculation of the subsequent bit level,
and is
≥
2
t
Q
. At the sample point, the bus level is read and interpreted as the value of
the bit cell. It occurs at the end of PHASE_SEG1.
The total number of
t
Q
in a bit time is specified to be between 8 and 25.
As a result of re-synchronization, PHASE_SEG1 can be lengthened or PHASE_SEG2
can be shortened. The amount of lengthening or shortening the phase buffer segments
has an upper limit given by the re-synchronization jump width. The re-synchronization
jump width may be between 1 and 4
t
Q
, but it may not be longer than PHASE_SEG1.
MCA05830
Sample
Point
Synchronisation
Segment
(SYNC_SEG)
Propagation
Segment
(PROP_SEG)
Phase Buffer
Segment 1
(PHASE_SEG1)
Phase Buffer
Segment 2
(PHASE_SEG2)
Nominal Bit Time
