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If a star configuration is unavoidable, special RS-485 repeaters are available which bidirectionally listen for data on each span and then retransmit the data onto all other spans. Although total cable length maybe shorter in a star configuration, adequate termination is not possible anymore and signal quality may degrade significantly. However, it is important to note that as the length of the cable increases, signal distortion can occur during transmission along the communication line, thereby reducing the maximum data rate that can be achieved. PURPOSE AND SCOPE OF COVERAGE - This standard is intended to provide a method of interconnecting data terminal equipment and a data communication channel when each is furnished by different companies. This "third wire" is not officially part of the standard and is discussed further in the grounds and grounding section. This installation should have a third wire connecting the earth ground/circuit common from the desktop PC to the laptop's RS-485 port circuit common. Within such a system, RS-485 serves a pivotal role as a bridge, establishing communication of flow information between the central control system and each valve box. The flow meters relay flow information in real-time to the central control system via RS-485, halting the supply once the specified amount of reagent is dispensed.

In the central chemical dosing and dispensing system of China's Hingsen Semiconductor, the configuration comprises central chemical storage tanks coupled with dispensing systems at each process point, RS485 standard controlled through valve boxes to regulate the supply of chemical reagents. These signals are integrated with the customer's central control system, allowing for the retrieval of relevant flow measurement data through the central control system's associated software and settings. Devices utilizing RS485 can communicate with central control systems using communication protocols such as Modbus and ASCII. Therefore, RS-485 can be described as a hardware architecture that does not specify or recommend any transmission protocols but solely defines the electrical characteristics of transmitters and receivers. Among various topological structures, the Daisy Chain topology is considered the optimal choice for RS-485 due to its minimal impact on signal integrity. 1) The signal level value of the interface is high, which is easy to damage the chip of the interface circuit. It is not compatible with TTL level, so it needs to use level conversion circuit to connect with TTL circuit. 3V as logic "0", signals lower than -3V as logic "1", TTL level of 5V is logic positive, and 0 is logic negative.

6V, and logic "0" is represented by the voltage difference between the two wires -6V to -2V. This means there will be times when no driver is connected to the wires. The logic function of the driver and receiver are not defined, only the binary state of the differential voltages on the wires. Differential signals and twisting allows RS485 to communicate over much longer communication distances than achievable with RS232. 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. Because of this, the resulting noise current is many factors lower than with an ordinary straight cable. A gateway that converts the RS-485 data to run over an existing network may cost less in the end than running a kilometer of cable. Below is a common schematic diagram of an RS-485 circuit. With RS485 on the contrary there is no such thing as a common zero as a signal reference. But, it should be noted that the network running in the reference was running at 300 baud and had other tweaks such as isolated transceivers and high resistance bias resistors on every node.

This problem can also be fixed by adding bias resistors to force the line to idle condition when a driver is not connected, but this has to be done on a network basis, not a device basis. Galvanic isolation will break a large problem into several small, but manageable ones. Because there is a chance of data collosion with this implementation, theory tells us that in this case only 37% of the bandwidth will be effectively used. The RS232 interface conforms to the serial data communication interface standard established by the Electronic Industries Alliance (EIA) of the United States. 3V are undefined by the standard. The magnetic fields are allowed to pass, but do no harm. In other words, between Devices A and B, within a given time frame, only Device A is allowed to transmit data to Device B. Following the completion of this transmission, data transfer from Device B to Device A can then commence.