Difference between RS-232 and RS-485 > 자유게시판

RS-485 is known to be the advancement of RS-232 that supports technological upgradations. The physical setup defined by RS-485 standard supports multiple protocols, though not all operate on the network at the same time. Currently available high-resistance RS485 inputs allow this number to be expanded to 256. RS485 repeaters are also available which make it possible to increase the number of nodes to several thousands, spanning multiple kilometers. Yes, it is possible to use RJ45 connectors for RS-485 communication. It’s reasonable to question why one wouldn’t simply transmit signals at the quickest possible speed to hasten network updates.The answer lies in the degradation of communication signals due to transmission losses on the cable when the product of the communication trunk length and the baud rate exceeds the recommended limit. Without balance, unnecessary impedance may be added to wires and disrupt signals causing failed communication. The standard 120-Ω value for termination resistors corresponds to the differential-mode characteristic impedance of the twisted-pair bus wires.

Bus Probes are a family of low-power environmental sensors with an RS485 interface. Therefore the trigger level of the RS232 interface is set relatively high at ±3 Volt. Polarity: Set the network polarity accurately to ensure correct signal transmission.Termination: Proper network termination is vital to avoid signal reflections, which can lead to communication errors.Biasing: Biasing is beneficial for maintaining signal quality over long distances. Such cabling standards are set by organizations like the Electronic Industry Association (EIA) and the Telecommunication Industries Association (TIA). The EIA has officially disbanded and the standard is now maintained by the TIA as TIA-485, but engineers and applications guides continue to use the RS-485 designation. RS-485 is a great standard for serial transmission networks up to 100Mbps and operating in noisy environments. Why 120 ohm is used in RS-485? It is the reason why RS485 is so popular with computers, PLCs, micro controllers and intelligent sensors in scientific and technical applications.

Why is RS-232 still used? Additionally, many legacy systems still use RS-232, and upgrading to newer protocols may not be feasible or cost-effective. This makes RS-485 systems highly resistant to common-mode noise. RS485 is widely used in industrial control systems and can handle up to 32 devices on a single network. Basic termination networks, such as standard parallel termination networks, typically employ a single resistor. A 120-ohm termination resistor is commonly used in RS-485 communication to match the impedance of the transmission line and reduce signal reflections, which can improve the reliability of the communication. Otherwise, impedance will build preventing fidelity of signals expecting defined terminations for proper transmission. Any number of characters can be sent, and the transmitter will automatically re-trigger with each new character (or in many cases a "bit-oriented" timing scheme is used in conjunction with network biasing for fully automatic operation, including any Baud rate and/or any communications specification, eg. RS-485 is used as the physical layer underlying many standard and proprietary automation protocols used to implement industrial control systems, including the most common versions of Modbus and Profibus. Slaves Receive: All devices on the network, including the slave devices, constantly monitor the voltage difference between lines A and B. When they detect a change, they interpret this as a bit of data.Slave Responds: If the master device sends a command that requires a response from a slave device, that slave device will wait until the master has finished transmitting, then change the voltage difference between lines A and B to send its response.Master Receives: The master device, like the slaves, is constantly monitoring the voltage difference between lines A and B, so it will receive the response from the slave.

Consider how far devices will locate from the master as this will determine transmission, or baud, rate of your network. For both other interfaces-RS422 and RS485-the slew rate is indefinite. RS232 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 standard defines up to 100Mbps clock rate for RS-485 although slower clocking is required for longer cable lengths defined in the standard. RS-485 is a telecommunication standard describing physical attributes used for serial communications. With full duplex, this part is applicable for high-speed serial communications such as motion control, encoder interfaces, field bus networks, industrial control systems, and backplane busses. 12kV contact discharges on the transceiver bus pins without latch-up or damage. The standard provides the ability to configure more than one master on the bus with the caveat that only one master be active at any one time. To develop ideas, each vendor provides an evaluation board as well. This RS-485 transceiver provides high-speed operation over long distances at up to 100Mbps. The part incorporates integrated protection up to 15kV ESD human body model.

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