Modbus standard also defines Modbus over Serial Line, a protocol over the data link layer of the OSI model for the Modbus application layer protocol to be communicated over a serial bus. It does not specify or recommend any communications protocol; Other standards define the protocols for communication over an RS-485 link. RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. Reserved Function Codes are function codes used by some companies for legacy product and are not available for public use. The equipment located along a set of RS-485 wires are interchangeably called nodes, stations or devices. Ideally, the two ends of the cable will have a termination resistor connected across the two wires. From the latest point of view, advancements in technology have led to the development of enhanced RS485 cables that can support even higher transmission speeds and longer distances. This has led to the development of enhanced shielding techniques and improved cable designs to minimize signal loss and maintain signal integrity over longer distances.

In addition to its physical characteristics, RS485 cables also have specific electrical properties that allow for differential signaling, enabling reliable data transmission over longer distances compared to other communication protocols. RS-485 cables typically have two twisted pairs of wires for differential signaling, allowing for greater immunity to electromagnetic interference. This allows RS-485 to implement linear bus topologies using only two wires. In a computer system, SCSI-2 and SCSI-3 may use this specification to implement the physical layer for data transmission between a controller and a disk drive. In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. This section also defines the logic states 1 (off) and 0 (on), by the polarity between A and B terminals. If A is negative with respect to B, the state is binary 1. The reversed polarity (A positive with respect to B) is binary 0. The standard does not assign any logic function to the two states. What are the two end-nodes? The cabling is done such that all these devices are connected in parallel. All communication cabling to be installed in a daisy chain configuration, no T’s are permitted.

They also provide the parameters for communication for this particular controller, and it’s predecessor, here. From what I’ve read, the modbus is a protocol for communication between a computer and an RS485 device, if this is true, I shouldn’t need a modbus lib for this application. TSB-89A, Application Guidelines for TIA/EIA-485-A does not recommend using star topology. The foreword to the standard references The Telecommunications Systems Bulletin TSB-89 which contains application guidelines, including data signaling rate vs. Transmission speed refers to the rate at which data is transferred between devices using the RS485 cable. Insulation/separator layer: This layer plays a role in insulation and enhances the durability and lifespan of the cable. RS-485 only specifies the electrical characteristics of the generator and the receiver: the physical layer. The outer layer of aluminum foil covers the entire conductive core, serving to counteract high-frequency interference. The physical characteristics of an RS485 cable include twisted pair conductors, typically two or four, which help reduce electromagnetic interference and improve signal integrity. The rs485 shielded cable is known for supporting multi-point communication, meaning multiple devices can be connected to the same network, facilitating versatile and complex setups.

Since RS-485 is a multi-point specification, however, this is not necessary or desirable in many cases. 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. RS-485 signals are used in a wide range of computer and automation systems. RS-485 is used for low-speed data communications in commercial aircraft cabins' vehicle bus. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422. The electrical characteristics of RS485 cables include differential signaling, which allows for high noise immunity and long transmission distances of up to 1200 meters. It is designed to transmit data over long distances and in noisy environments. LAPP UNITRONIC ® BUS LD cables are built after the RS-422 and RS-485 standards and are robust solutions for transmitting data over long distances and noisy environments. LAPP UNITRONIC ® BUS LD FD P cables are built after the RS-422 and RS-485 standards and are robust solutions for transmitting data over long distances and noisy environments.