Now, let me tell you about some key serial communication characteristics.
First, we have synchronous and asynchronous serial communication, where synchronous may mean that
this type of communication requires one channel to carry the clock signal, that clock signal will tell
both the transmitter and the receiver that one bit is being sent, whereas asynchronous means that this
communication type does not require a clock signal.
So an asynchronous serial communication interface may require just one line to transmit data.
So that would mean that the transmitter and the receiver may communicate by whatever number of lanes
plus a clock line.
So whether or not we are using this clock lane determines if we are using a synchronous or asynchronous
serial communication interface.
Next, we have one way and two way serial communication.
By that, I mean that if one device can only transmit and the other can only receive them, data goes
from one device to another, which would be one way.
But if both devices can communicate with each other, then we would have bi directional communication.
So if we have a device, A and a device B, we may be able to send data from A to B and from B to A.
This would be bi directional and bidirectional communication can be either half duplex or full duplex.
So full duplex means that when a is transmitting something to be B might be transmitting something to
a.
So this would be a true bi directional system, but we may have half duplex communication also.
And that is that whenever a is transmitting something to be B cannot transmit to a each transmission
has to occur in its own time exclusively.
They might even share one line for sending or receiving data like this.
So this shared land would be used to send data from A to B or from B to A, but only one transmission
can occur in a given point in time.
We also have the number of lines that are required for a serial communications interface.
So in this first example, I am using two lines one for the data and one for the clock signal.
So this would require two lines, but this is one directional.
Whereas here I would be using two lines to send and receive data from a standpoint, and we might use
a clock signal and some other arbitrations signals.
And so the number of lines required is definitely a parameter here.
We also have the electrical characteristics of serial communication, so there are serial communication
interfaces that are intended to communicate integrated circuits on a board.
For example, spy and ice where.
And those simply required to comply with the supply voltage or the logic levels of the chips you want
to communicate.
But some other standards, like the asynchronous serial communication interface from legacy computers
that one uses a standard known as RSA 232, which uses different logic levels than those used on a PCB
for chips.
For example, in RC 232, a logical zero is something around plus 12 volts, and a logical one is about
minus 12 volts.
So this is definitely different than the logical one used in CMOs chips that could be 3.3 volts and
zero would be zero volts.
Anyway, there are electrical characteristics other than the voltage.
We have timing characteristics, power specifications, impedance and so on and so forth.
We also have differences in the networks that can be implemented with different serial communications
interfaces.
For example, we have the role of masters and slaves in a network that is elements that have control
over the communication that's going on in the bus and the other elements that simply obey to those commands
emitted by the Masters.
We have addresses where each device may have its own address, and different devices can communicate
with each other by means of those addresses.
We have the topology of the network.
Some serial communication interfaces may only support a daisy chain topology, for example, whereas
others may support a star topology.
So as you can see, there are many factors that determine how we are going to implement our serial communications
interface.
And so all of the different standards came from the manufacturers choosing different parameters for
their intended applications.