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RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422. RS232 allows both communicating parties to transmit and receive data at the same time; this is referred to as full duplex communications. As it is a half-duplex IC hence it can not both transmit and receive at the same time. Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. The RS485 protocol uses differential data signals for improved noise immunity; thus RS485 can communicate over greater distances than RS232. The cabling of the industrial communication systems (Modbus RS485) is different in some ways from the cabling used for power cabling and the electrician may experience some difficulties if he is not an expert in Modbus communication networks. By using repeaters very large RS-485 networks can be formed. 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. For this reason, frame-level cyclic redundancy checks are much more widely used for validating data from serial links, network connections and storage media. All of the serial ports are supported by pre-coded C-language software drivers that make it easy to exchange data.

The Serial1 and Serial2 ports have identical communications capabilities, although more of the Serial1 signals (both RS232 and RS485) are made available on the Docking Panels headers and connectors. The RS485 system used for Modbus communication provides a main cable (Bus or backbone), to which all the devices have to be connected with branches (also known as stubs) that are as short as possible. Characters may be lost if the transmit driver is turned off while pending characters are still being transmitted. The termination also includes pull up and pull down resistors to establish fail-safe bias for each data wire for the case when the lines are not being driven by any device. This way, the lines will be biased to known voltages and nodes will not interpret the noise from undriven lines as actual data; without biasing resistors, the data lines float in such a way that electrical noise sensitivity is greatest when all device stations are silent or unpowered. It also defines three generator interface points (signal lines); A, B and C. The data is transmitted on A and B. C is a ground reference.

Section 4 defines the electrical characteristics of the generator (transmitter or driver), receiver, transceiver, and system. This section also defines the logic states 1 (off) and 0 (on), by the polarity between A and B terminals. At the UART, a logic high (5 volts) is called a mark, and a logic low (0 volts) is called a space. The equipment located along a set of RS-485 wires are interchangeably called nodes, stations or devices. Unlike what happens in many energy distribution systems, rs485 cable the manner in which the devices are connected in parallel is important. A Modbus RS485 connects a Master device to one or more Slave devices. In the most common multi-drop RS485 protocol, one computer is designated as a master and the rest of the computers or devices on the serial bus are designated as slaves. Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance. This allows RS-485 to implement linear bus topologies using only two wires. Ideally, the two ends of the cable will have a termination resistor connected across the two wires.

RS-485, like RS-422, can be made full-duplex by using four wires. In summary, the code provided for implementing the second serial port is very flexible and can be used to support dual concurrent communications ports. When PE is set (equal to one), the most-significant bit in each byte transmitted will be a parity bit that is either set or cleared by the serial port automatically in order to achieve even or odd parity. A jumper labeled "1 485En" (J4) enables RS485 operation on the Serial1 port if the jumper cap is installed, and configures Serial1 for RS232 operation if the jumper cap is not installed. The snap switch located on the TSX08PRGCAB programming cable are used to choose a different mode of operation. The M bit, with mask 0x10, determines whether eight or nine bits total are transmitted with each byte, regardless of whether or not the most-significant bit is a parity bit. Converters between RS-485 and RS-232 are available to allow a personal computer to communicate with remote devices.