AcroPack Series AP560
CAN Bus Interface Module
- 39 -
Figure 8 CAN Bit Time
Phase Buffer Segment 1 and Phase Buffer Segment 2 (Phase Seg1 and Phase Seg2)
The phase buffer segments are used to compensate for phase errors on the
bus. Phase Seg1 can be lengthened or Phase Seg2 can be shortened during
the re-synchronization bit period automatically by the HI-3111 so that the bit
time can be adjusted to account for phase errors. The upper limit by which
the lengthening (or shortening) can occur is set by the
re-synchronization
jump width (SJW),
explained in more detail below.
Sample Point
The sample point is the point in the bit time at which the bit logic level is
interpreted. It is located at the end of Phase Seg1. The HI-3111 also allows
three sample points to be taken. In this case, two other sample points are
taken prior to the end of Phase Seg1 (at one-half TQ intervals) and the value
of the bit is determined by a majority decision. Three sample points are
typically only used at low bit rates.
Note:
ARINC 825 states that there shall be
only one sample per bit, taken at the end of Phase Seg1.
The time required for the logic to determine the bit level of a sampled bit is
known as the
information processing time (IPT)
. Per the standard, IPT can be
up to 2Tq. Since Phase Seg2 occurs after the sample point, Phase Seg2 must
be greater than or equal to the worst case IPT (2Tq).
Summary of Contents for AcroPack AP560
Page 28: ...AcroPack Series AP560 CAN Bus Interface Module 28 Figure 2 Standard Data Frame...
Page 30: ...AcroPack Series AP560 CAN Bus Interface Module 30 Figure 3 Extended Data Frame...
Page 32: ...AcroPack Series AP560 CAN Bus Interface Module 32 Figure 4 Remote Frame...
Page 34: ...AcroPack Series AP560 CAN Bus Interface Module 34 Figure 5 Error Frame...
