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One other key advantage that most people using 485 is, the better noise immunity. And the 485 is also very fast. RS485 main advantages as compared to other serial communication are tolerance to electrical noise, lengthy cable runs, multiple slaves in one connection, and fast data transmission speed. While the standard only supports low data rates and short line length (50ft.) it is still widely used and, very useful in many applications. Practically speaking you can go up to 4000 feet at baud rates up to 76800 baud. Its maximum cable length is 1200 meters that are about 4000 feet. Maximum length is 4000 ft. Some of the disadvantages of RS232 are the speed of the data can be transferred around 20 kilobytes per second, and the maximum length of cable is about 50 feet. Other elements like wire gauge, biasing circuit characteristics (impedance or capacitance), the existence of stubs from the main trunk, what is rs485 cable and the physical arrangement of your network cable can all affect your network’s maximum length.Take into account all these factors and maintain a buffer to stay within the advised limit for the overall max network cable length.

The resistance of the twisted pair cable will drop the voltage difference as it travels down the wire. When the receiver reads the voltage on the other end there could be as little as 0.2 volts difference between the two wires. For a more detailed discussion read WHY YOU NEED 3 WIRES FOR 2 (TWO) WIRE RS485 FOR BACNET. EIA-485 (formerly RS-485 or RS485) is a specification for the physical layer of a network that uses the difference in voltages between two wires (Three wire) to conveys data. Modbus defines a protocol data unit (PDU) independently to its lower layer protocols in its protocol stack. BACnet MSTP uses RS485 (also known as EIA485) as it physical layer. Here is a question for you, what are the features of RS232 and RS485? One common example that many people probably know that is a computer connected to a printer, the RS232 is widely used for printers in working places. The remaining "inactive" slaves may actively receive, or listen to, data on the communications line, but only one slave at a time can transmit a message. The specifications and configurations of RS485 make faster and extend the data transmission range. Search the Internet on RS485 you will find Bob Perrins's article called THE ART AND SCIENCE OF RS-485.

It is his reference to Art that makes RS485 bad. This is good and bad. In addition there is no good way to add terminations resistors at the ends of a "star" network. Termination resistors also reduce electrical noise sensitivity due to the lower impedance, and bias resistors are required. The recommended arrangement of the wires is as a connected series of point-to-point () nodes, a line or bus, Ideally, the two ends of the cable will have a termination resistor connected across the two wires. 0.2 is the minimum recommended voltage difference that receivers use to detect a change in polarity. In this article, the difference between RS232 and RS485, advantages and disadvantages of RS232, advantages, and disadvantages of RS485, basics of RS232, basics of RS485 are discussed. You can use the QED Board’s RS485 link to create such a multi-drop serial network. The SCK (serial clock) pin is a configurable synchronous data clock output. If the 68HC11 is initialized as a master by setting the MSTR bit, then bit 5 of the Port D data direction register (PORTD.DIRECTION) determines whether /SS is an input or an output. When the 68HC11 controls the network, it is referred to as a "master"; otherwise, it is a "slave".

Although the devices would share the same network, communications would only be understandable by members of the same group. As it is a half-duplex IC hence it can not both transmit and receive at the same time. RS485, CAN bus to build network with both of the signal/power in two wires (total bus can provide 960 watt power and 12 watt in every terminal). The more power sources used to power devices, the greater the physical separation of devices, the less well-grounded devices, and power sources are the greater the risk. Those include, interface connector, mapping, interconnection, conversion, measurement, protection and power amplification hardware accessories. It doesn’t have a standard connector, so many times the old DB-9 connector is used. Many times the old DB-9 connector is used. In most cases the times are less than 25 µs which does not pose a problem. While it goes against conventional wisdom, and can potentially cause a problem with circulating currents by grounding a shielded cable at both ends, this method is very effective at keeping induced lightening noise away from the communications lines.