Civil Engineering Reference
In-Depth Information
Fig. 2.25
Different intense ringing at the “dominant-to-recessive” transition
acknowledge except the frame sending node. As a result of this, there are many
energy input points in the system and with it a lot of energy in the system.
Ringing occurs more heavily when the topologies consist of stars or of stubs with
long stub length as well as when the topology has a symmetric shape. In this case,
the more intense ringing is a result of reflections and adding of reflection parts in
the case of symmetric shapes.
The effects of the ringing can be seen in the delay times. A view on the thresh-
olds helps the valuation of the ringing: If the differential bus signal exceeds 0.9 V,
caused by an overshoot, this will lead to a change of the logic RxD to the dominant
state until the differential bus signal falls back below 0.5 V (worst-case threshold
values). In this case, the ringing drives a change on the logic signals which results
in a prolongation of the related system propagation delays.
2.2.3.2
GND Shift, CMC and Arbitration
With the help of a further example, it is possible to observe the effect of self-induc-
tion on the CAN bus. In the case of a lost arbitration, the state of the node changes
from sending to receiving. Based on a scenario with two nodes sending a dominant
bit followed by a dominant bit of the arbitration winning node and a recessive bit
by the arbitration losing node, the direction of the energy flow changes at the losing
node (from driving energy by sending a dominant bit to receiving energy by receiv-
ing a dominant bit of a foreign node). As a consequence, there is a reverse of the
energy flow in the CMC as well.
