Civil Engineering Reference
In-Depth Information
Fig. 2.17
Optional ECU 6 increases the propagation delay (220 ns
480 ns) due to the symmetry
of the topology
The waveforms also show very clearly that the signal quality is heavily influ-
enced by the position in the system. It is not sufficient to analyse a single position in
the network. Since the access of measuring points in the final system is very limited,
the signal analysis by means of simulations is often the only solution.
2.2.2
Architecture of CAN Nodes
The previous chapter addressed the influences of the characteristics of network ar-
chitectures. In this chapter, the architecture of a CAN node and its components shall
be handled. In this context, all components taking part in the signal transmission
from a digital to an analog CAN bus signal and vice versa are inquired. Function-
ing and implementation reasons as well as signal integrity crucial attributes are
explained.
2.2.2.1
CAN-Bit-Timing and Oscillator Tolerances
The interface between the physical layer and the data link layer are the digital sig-
nals RxD and TxD. With the help of these signals, information is given over to the
other respective communication layer. This is only possible if both sides are using
the same comprehension of the information content. In case of the RxD and TxD
signals, this is reduced to the binary logic with both its defined states logic “1” and
logic “0”. However, there is a further physical unit which is present at the interface
between the physical and data link layer and shall be considered: the time. In this
case, the timing aspect is interesting regarding the oscillator tolerances inside the
protocol layer and different delay times in the physical layer. Through the configu-
