How does the hardware work? Data is transmitted differentially on two wires twisted together, referred to as a "twisted pair. A network can be configured two ways, "two-wire" or "four-wire. The "slave" transmitters are all connected to the "master" receiver on a second twisted pair. In either configuration, devices are addressable, allowing each node to be communicated to independently. Only one device can drive the line at a time, so drivers must be put into a high-impedance mode tri-state when they are not in use.
Some RS hardware handles this automatically. In other cases, the device software must use a control line to handle the driver. If your device is controlled through an RS serial port , this is typically done with the RTS handshake line. A consequence of tri-stating the drivers is a delay between the end of a transmission and when the driver is tri-stated.
This turn-around delay is an important part of a two-wire network because during that time no other transmissions can occur not the case in a four-wire configuration. An ideal delay is the length of one character at the current baud rate i. The device manufacturer should be able to supply information on the delay for their products. Two-wire or four-wire? Two-wire networks have the advantage of lower wiring costs and the ability for nodes to talk amongst themselves.
On the downside, two-wire mode is limited to half-duplex and requires attention to turn-around delay. Four-wire networks allow full-duplex operation, but are limited to master-slave situations i. How does the software work? Determine before any purchase whether your software handles these features. Remember, too much or too little turn-around delay can cause troubleshooting fits, and delay should be a function of baud rate.
If you're writing your own software or using software written for an RS application, be certain that provisions are made for driver tri-state control. Luckily, there are usually hardware alternatives for controlling driver tri-stating. Connecting a multidrop network. Reversing the polarity will not damage a device, but it will not communicate.
This said, the rest is easy: always connect A to A and B to B. Signal ground, don't forget it. While a differential signal does not require a signal ground to communicate, the ground wire serves an important purpose. Over a distance of hundreds or thousands of feet there can be very significant differences in the voltage level of "ground. If the grounds differ more than that amount, data will be lost and often the port itself will be damaged.
The function of the signal ground wire is to tie the signal ground of each of the nodes to one common ground. However, if the differences in signal grounds is too great, further attention is necessary. Optical isolation is the cure for this problem. Western Sahara Yemen Zambia Zimbabwe. Learning Center. Please note our new company name. Basics of the RS Standard. Download White Paper. Newsletter Signup phone: email: info advantech-bb.
Cellular Routers. AirborneM2M WiFi Wzzard Wireless Sensing Platform. Wireless Accessories. Industrial PCs. Standmount Embedded Automation Controllers. The multiple drivers and receivers are connected in RS, and the bidirectional communication can be seen in a single cable. It allows bidirectional transmission of data with high speed through one cable and the cable needs two terminations. Due to the inclusion of network topology, it is a renowned serial port in data acquisition systems and some control applications.
This is the only serial port that can easily make interworking with various transmitters or drivers and receivers in the same network. When the input resistance of RS is 12Kohm, the network can connect more than 32 receivers or transmitters. After using high resistance, the capacity of transmitters on the same network will be increased, and it can be increased up to The same thing can be seen in the case of receivers.
It is also extendable. It is one of the effective pot while connecting computers, PLCs, and different kinds of microcontrollers. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Notify me of new posts by email. Don't subscribe All Replies to my comments Notify me of followup comments via e-mail. You can also subscribe without commenting.
Despite the wide variety of modern alternative solutions, today RS technology remains the basis of many communication networks. The major advantages of RS interface are: Two-way data exchange via one twisted pair of wires; support for several transceivers connected to the same line, i. Serial data stream can be transported in one direction, data transfer to the other side requires using a transceiver.
A transceiver commonly referred to as 'driver' is a device or an electrical circuit that forms a physical signal on the transmitter side. Receiving or transmitting data requires two equivalent signal wires. The wires are used to exchange data in both directions alternatively. With the help of a twisted pair cable, the symmetrical channel significantly increases the stability of a signal and suppresses electromagnetic radiation generated by the useful signal.
RS communication line can work with multiple receivers and transceivers connected. At the same time, one transmitter and several receivers can be attached to one communication line at a time. All the other transmitters that need to be connected should wait until the communication line is free for data transmission. One of the main features that differs RS communication from any other serial communication is the format of data exchanged.
Modbus is a serial communications protocol that is widely used by industrial electronic devices. Modbus helps access the configuration of the devices and read the measures. The data exchange is initiated by a host. The host can switch its RS driver to the transmission mode on its own, while the other RS drivers slaves work in the receiving mode.
In order for a slave to answer the host over the communication line, the 'master' sends it a special command, which gives the intended device the right to switch its driver into a transmission mode for a certain time. Modbus is one of the simplest protocols for the interaction of devices with each other.
It is at the same time easy to implement for equipment manufacturers, which is the primary reason for its prevalence, and at the same time, it is difficult for an engineer, programmer, because it shifts onto his shoulders all the difficulties of implementation in the final solution, requiring him to work with multi-page tables of registers and variables, their addresses, various functions of writing and reading and data conversion.
The RS and RS serial communication protocols have been in use for over 50 years and are still widely used throughout business and industry.
Expanding the capabilities of the RS standard was the impetus for developing the RS protocol. The following table provides an overview of the two standards. The RS Serial Interface is designed to connect two devices. The protocol enables communication between a single transmitter and receiver.
Using an RS interface, up to 32 serial devices can be connected to one transmitter. Conversion enables older devices to coexist with new hardware that lacks serial interfaces. 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.
This length can be extended if slower data rates can be tolerated. The operation distance is substantially extended in the RS protocol. It supports maximum data rates at a length of meters, making the RS protocol an excellent choice for communication between physically distant pieces of equipment. An RS interface is a system based on voltage levels and performs optimally in situations where there are minimal differences in ground potential.
The RS protocol employs a differential voltage system that allows it to operate effectively in environments with higher levels of electrical noise.
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