The RS protocol employs a differential voltage system that allows it to operate effectively in environments with higher levels of electrical noise. A byproduct of the differential voltage system is the extended data transfer distance, increased transmission speed, and lower voltage use seen with RS Eltima IBC uses cookies to personalize your experience on our website.
By continuing to use this site, you agree to our cookie policy. Click here to learn more. Olga Weis Oct 20, Contents What is RS? How far can you run RS? What is RS communication protocol? RS communication: main features What is Modbus protocol? RS vs RS Comparing serial communication protocols.
RS Data Analyzer. Working with serial apps and devices, specialists often rely on dedicated software, like RS Data Logger by Electronic Team, to sniff and analyze serial port activity, detect errors, compare received data, etc.
Serial Port Monitor. Download day fully-functional trial period. What is RS? RS communication: main features Despite the wide variety of modern alternative solutions, today RS technology remains the basis of many communication networks. Bi-directional half-duplex data transmission Serial data stream can be transported in one direction, data transfer to the other side requires using a transceiver. Symmetrical communication channel Receiving or transmitting data requires two equivalent signal wires.
Multi-pointing RS communication line can work with multiple receivers and transceivers connected. What is RS Modbus protocol? RS vs RS Comparing serial communication protocols The RS and RS serial communication protocols have been in use for over 50 years and are still widely used throughout business and industry.
Operational Distance Devices using the RS protocol are limited to a distance of 15 meters between transmitter and receiver while still achieving the maximum data transmission rate. Electrical Noise Concerns and Ground Potential An RS interface is a system based on voltage levels and performs optimally in situations where there are minimal differences in ground potential. Frequently Asked Questions. The physical layer is the communication channel and the signal transmission method level 1 of the OSI open system interconnection model.
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Latest version. This transmitter creates the differential pair to be sent out over the cabling. With two signals generated, the receiver no longer references the voltage level to ground, but instead references the signals to each other.
This means that rather than looking for specific voltage levels, the receiver is always looking at the difference between the two signals. The differential receiver then reconstructs the pair of signals back into one single-ended signal that can be interpreted by the host device using the proper logic levels required by the host, Figure 3. This type of interface also allows devices of differing voltage levels to operate together by way of communication between the differential transceivers.
All this works together to overcome the signal degradation that would have occurred with a single-ended application over long cabling distances.
Signal degradation is not the only issue that arises over long cabling distances. The longer the cabling is within a system, the higher the chances that electrical noise and interference will make its way onto the cables and ultimately into the electrical system.
When noise couples onto cabling it shows up as voltages of varying magnitudes, but the benefit of using a balanced twisted pair cable is that the noise couples to the cable equally on each line. Because the differential receiver subtracts the signals from each other to get the reconstructed signal, it would ignore the noise shown equally on both wires, Figure 4. The ability of the differential receiver to ignore voltages that are the same on both signal lines is referred to as common mode rejection.
One of the other major physical layer benefits of RS is the signal voltage specification. RS does not require the use of a specific bus voltage, but instead specifies the minimum required differential voltage, which is the difference between the signal A and B voltages.
This means that any RS device is able to receive the voltage range of -7 to 12 V, so an engineer can design the host system with any transmission voltage in that range. This allows designers to create RS systems using their existing board voltages.
With that being said, it is important to verify the product specifications to ensure that the device supports the full voltage range of the standard. However, they are also input tolerant between 0 and 12 V.
This is especially important because as cable length increases, so does the voltage drop on the signal lines.
RS is a duplex communication system in which multiple devices on the same bus can communicate in both directions. In half-duplex, devices take turns using the same line where the host will assert control of the bus and send a command with all other devices listening. The intended recipient will listen for its address and then that device will assert control and respond back. It is connected to the RS differential transceiver that makes up the physical layer and converts the signals into the half-duplex differential format for use on the RS bus.
The host will then communicate with the RS through the UART, and it will tell the transceiver when to switch between transmit and receive.
Slave devices will also use their UART in the same way. UART having dedicated transmit and receive lines allows it to operate as full-duplex, half-duplex, or even simplex, which means data only ever goes out or comes in on one line. A UART interface is asynchronous which means that the communication does not include a clock. The host and slave devices must use their own internal clocks, and both devices must know at which clock-rate the data will be transmitted. This differs from a synchronous system such as Serial Peripheral Interface SPI where one of the signal lines contains a clock on which the listening device on the bus can capture data.
In addition, the UART generally has a normal format that most devices will use, but many options can be configured to change the norm. The idle state of UART is voltage high, so to begin transmission the UART uses a low pulse called a start bit, followed by 8 bits of data, and is completed with a high stop bit, Figure 8.
Immediately after the data leaves the transceiver, the host switches the mode of the transceiver to receive. When the slave is ready to respond, it transmits as the host did originally while the host now receives, Figure 9. The network layer deals with the actual communication between devices that occur on the RS bus. Because RS is mostly an electrical specification, the conversation could end here, but as it supports multi-drop, there is a need to address it in the OSI model.
There is no set specification for addressing the network layer, but the RS bus must be properly managed by a master to avoid bus collisions. Bus collisions occur when multiple devices attempt to communicate at once, which can be very harmful for the network. When collisions occur, transmitters clash on both ends and effectively both create shorts.
This causes each device to draw large amounts of current that could put the transceiver into thermal shutdown. To avoid collisions, the master controls the bus and will make calls to individual devices.
This is most often accomplished by having a command set that only specific devices recognize, or by having specific addresses for each device. The OSI model is not a set of rules but more of a model that helps engineers characterize systems.
RS is well-contained within the first three layers of the OSI model with the actual implementation of the bus being characterized within the application layer. This layer covers the addresses or command sets used by the devices as well as the interpretation of the data. Once you start monitoring a required RS interface, all data transmitted through it is shown in real time. Thanks to this option, you can timely resolve any problem that arises in your serial communication network.
Monitoring multiple COM ports at a time. With that, the captured data will be saved to a single log. Simulating serial communication. The Terminal mode option allows you to emulate sending particular data in different formats string, binary, octal, decimal, hexadecimal, mixed. The RS loopback feature offered by the software is particularly useful for sessions comparison.
Electronic Team, Inc. By continuing to use this site, you agree to our cookie policy. Click here to learn more. Olga Weis Sep 20, Software solution: RS Data Logger. Serial Port Monitor. Download day fully-functional trial period.
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