 Introduction - Digital Technology 4
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This time, we will start with a very important term for this chapter, namely sampling rate. It has something to do with information being passed on sensibly. This can be explained using a simple example.
She in her room in the parental home in, say, 1960. Cell phones do not yet exist. He in the park next door, both equipped with flashlights. There is already a fixed meeting place. The only thing left to decide is
when to meet the next day.
If it's in the afternoon, that's already more than 12 light signals. If he doesn't notice a light signal in the park, he's an hour early. Yes, of course, control mechanisms could be introduced, as is done in
digital technology, but that would overwhelm this example.
But perhaps you already understand how important the sampling rate is. The voltage pulse sent must be significantly below a certain value at zero and must be above it at one. In between, the signal is indifferent.
The impulse must also remain stable for a certain period of time, meaning its rise or fall must be essentially complete by then. Imagine that the receiver is scanning while the signal is still in development. Actually unusual
for electricity, the pure square wave signal.
But it has to be that way, because height matters in order to be able to clearly distinguish between low and high; otherwise, it doesn't matter, unlike with analog technology. Sometimes the time in between counts, but more
on that later, e.g., in pulse width modulation.
This is only about synchronous behavior, which is achieved, for example, by a fixed sequence of, say, ten ones at the beginning, also known as synchronization. At the same time, the length of the pauses is also practiced.
This is actually unthinkable in human communication, even though we sometimes have difficulty when the person we are talking to speaks so terribly fast. Does that mean everything is settled if each bit is transmitted
cleanly?
Of course not. What are you supposed to do with zeros and ones? You have to imagine a net. Let's take the single-wire CAN bus, i.e., a data line and ground, which is very rare but well suited for our purposes.
Important, this goes to several participants, who can even access it, at least to pick up on initial impulses. But it's like YouTube, only for channel members. This means that every message receives an address, and every
participant now actually intercepts it.
What do we have so far? Yes, a kind of preamble, so that every participant can synchronize and the possibility that a subsequent address can be decoded. This determines whether the
respective participant continues reading.
The LIN bus even has a master that also targets a specific address. However, it then keeps free an area in the data domain so that the participant can enter, for example, a measured value decoded in binary form there.
Such a master is not present in the CAN bus.
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