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Difference Between Rs232 And Rs422 Pdf

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RS is without doubt the best known interface, because this serial interface is implemented on almost all computers available today. But some of the other interfaces are certainly interesting because they can be used in situations where RS is not appropriate. We will concentrate on the RS interface here. This was sufficient in the old days where almost all computer equipment were connected using modems, but soon after people started to look for interfaces capable of one or more of the following:. RS is the most versatile communication standard in the standard series defined by the EIA, as it performs well on all four points.

RS-232 vs RS-422/485

RS is without doubt the best known interface, because this serial interface is implemented on almost all computers available today. But some of the other interfaces are certainly interesting because they can be used in situations where RS is not appropriate. We will concentrate on the RS interface here. This was sufficient in the old days where almost all computer equipment were connected using modems, but soon after people started to look for interfaces capable of one or more of the following:.

RS is the most versatile communication standard in the standard series defined by the EIA, as it performs well on all four points. That is why RS is currently a widely used communication interface in data acquisition and control applications where multiple nodes communicate with each other. One of the main problems with RS is the lack of immunity for noise on the signal lines. The transmitter and receiver compare the voltages of the data- and handshake lines with one common zero line.

Shifts in the ground level can have disastrous effects. Noise is easily picked up and limits both the maximum distance and communication speed.

With RS on the contrary there is no such thing as a common zero as a signal reference. Several volts difference in the ground level of the RS transmitter and receiver does not cause any problems.

The RS receiver compares the voltage difference between both lines, instead of the absolute voltage level on a signal line. This works well and prevents the existence of ground loops, a common source of communication problems. The image below explains why. In the picture above, noise is generated by magnetic fields from the environment.

The picture shows the magnetic field lines and the noise current in the RS data lines that is the result of that magnetic field. In the straight cable, all noise current is flowing in the same direction, practically generating a looping current just like in an ordinary transformer.

When the cable is twisted, we see that in some parts of the signal lines the direction of the noise current is the oposite from the current in other parts of the cable. Because of this, the resulting noise current is many factors lower than with an ordinary straight cable.

Shielding—which is a common method to prevent noise in RS lines—tries to keep hostile magnetic fields away from the signal lines. Twisted pairs in RS communication however adds immunity which is a much better way to fight noise. The magnetic fields are allowed to pass, but do no harm. If high noise immunity is needed, often a combination of twisting and shielding is used as for example in STP, shielded twisted pair and FTP, foiled twisted pair networking cables.

Differential signals and twisting allows RS to communicate over much longer communication distances than achievable with RS Differential signal lines also allow higher bit rates than possible with non-differential connections.

Therefore RS can overcome the practical communication speed limit of RS What does all the information in this table tell us? We also see that there is a maximum slew rate defined for both RS and RS This has been done to avoid reflections of signals. The maximum slew rate also limits the maximum communication speed on the line.

For both other interfaces—RS and RS—the slew rate is indefinite. To avoid reflections on longer cables it is necessary to use appropriate termination resitors.

We also see that the maximum allowed voltage levels for all interfaces are in the same range, but that the signal level is lower for the faster interfaces. Interesting is, that RS is the only interface capable of full duplex communication. This is, because on the other interfaces the communication channel is shared by multiple receivers and—in the case of RS—by multiple senders. RS has a separate communication line for transmitting and receiving which—with a well written protocol—allows higher effective data rates at the same bit rate than the other interfaces.

The request and acknowledge data needed in most protocols does not consume bandwidth on the primary data channel of RS Network topology is probably the reason why RS is now the favorite of the four mentioned interfaces in data acquisition and control applications.

RS is the only of the interfaces capable of internetworking multiple transmitters and receivers in the same network. Currently available high-resistance RS inputs allow this number to be expanded to RS repeaters are also available which make it possible to increase the number of nodes to several thousands, spanning multiple kilometers. And that with an interface which does not require intelligent network hardware: the implementation on the software side is not much more difficult than with RS It is the reason why RS is so popular with computers, PLCs, micro controllers and intelligent sensors in scientific and technical applications.

In the picture above, the general network topology of RS is shown. N nodes are connected in a multipoint RS network. For higher speeds and longer lines, the termination resistances are necessary on both ends of the line to eliminate reflections. The RS network must be designed as one line with multiple drops, not as a star.

Although total cable length maybe shorter in a star configuration, adequate termination is not possible anymore and signal quality may degrade significantly. And now the most important question, how does RS function in practice? Default, all the senders on the RS bus are in tri-state with high impedance. In most higher level protocols, one of the nodes is defined as a master which sends queries or commands over the RS bus. All other nodes receive these data.

Depending of the information in the sent data, zero or more nodes on the line respond to the master. There are other implementations of RS networks where every node can start a data session on its own. This is comparable with the way ethernet networks function. With such an implementation of a RS network it is necessary that there is error detection implemented in the higher level protocol to detect the data corruption and resend the information at a later time.

There is no need for the senders to explicity turn the RS driver on or off. RS drivers automatically return to their high impedance tri-state within a few microseconds after the data has been sent. Therefore it is not needed to have delays between the data packets on the RS bus. RS is used as the electrical layer for many well known interface standards, including Profibus and Modbus. Therefore RS will be in use for many years in the future.

RS485, RS422 and RS232

It is widely used for computer serial interface peripheral connections. Connect cables and mechanical, electrical, signal, and transfer processes. The data transmission rate specified by the RSC standard is 50, 75, , , , , , , , , baud per second. RS is one of the mainstream serial communication interfaces. Due to the early appearance of the RS interface standard, it is inevitable that there are deficiencies, mainly the following four points:.

Let's see why it is still in use and why, at Robotiq , we decided to use it as the standard communication protocol for our devices. Many people are often confused when dealing with communication standards. Often, terms like ''RS'', ''USB'' and ''Ethernet'' are interchanged as if they could be switched and do the same job. It defines the electrical characteristics of the transmitter and the receiver. In the case of Ethernet and USB, these protocols define both the physical and application layer in their communication standard.


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RS485 serial information

RS and RS are standards for data cables. To exchange data between nodes on a network, the most commonly used tools are line drivers and receivers. It is difficult to set up a network with smooth data transfer if there is noise, ground level differences, mismatch of impedance and other dangers present. There are organizations like Electronic Industry association EIA and Telecommunication industries Association TIA that set the standards for the production of cables and other tools used in setting up of network.

First, lets define each one. Definitely the most popular interface, also being one of the first. However, things may soon change for obvious reasons. Any PC that is purchased will have one and sometimes more RS port.

Both Tx and Rx are referenced to a common ground. In other words: RS is voltage driven. Not a good engineering practice and well beyond the scope of our topic.

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Introduction to RS485

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What is the difference between RS422 communication and RS485 communication?

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