DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

is kept below 125 kbps, the bus can function if one of the two data wires is cut), whereas 1 –
Wire® has only a 16 – bit CRC; with CAN information being carried on the bus as a voltage
difference, this also gives the CAN bus a high immunity to electromagnetic interference,
whereas 1 – Wire® has data and power residing on the same line;
4.3.4 Timing Performance
One of the key elements related to the performance of any embedded system is message
latency. By definition, message latency is the time needed for an electronic message to travel
across a communications system and for the remote system to respond [63]. Message latency in
a packet-switched network is measured either one-way (the time from the source sending a
packet to the destination receiving it), or round-trip (the one-way message latency from source to
destination plus the one-way latency from the destination back to the source). Round-trip
message latency is more often quoted, because it can be measured from a single point. Where
precision is important, one-way message latency can be more strictly defined as the time from
the start of packet transmission to the start of packet reception [64]. This section presents an
analysis of the message latencies attributed with both communication protocols and possible
ways to minimize them.
Under CAN, a given message is assumed to be invoked by some event, and is then
given a bounded time for queueing of this message [65 – 66]. Because this time is bounded
instead of fixed, there is some variability, or jitter, between subsequent queuings of the message.
This is known as queuing jitter. It is assumed for the sake of analysis that there is a minimum
time between invocations of a given message (i.e. period). Since a given message is assigned a
97