Common questions

What is RS-485 full duplex?

What is RS-485 full duplex?

RS-485 is generally a 2-wire half duplex system. AN RS485 4-wire full duplex system is very similar to RS-422. RS485 is still popular. It is similar to the RS422 upon which it is based. The RS485 port has been used for many years.

What is RS-485 chip?

RS-485 allows multiple drivers on the bus for true bidirectional transmission over a single cable, so each Tx must have tri-state output capability. High-speed bidirectional transmission over a single cable requires two terminations.

What is RS-485 used for?

What is RS-485? RS-485 is an industrial specification that defines the electrical interface and physical layer for point-to-point communication of electrical devices. The RS-485 standard allows for long cabling distances in electrically noisy environments and can support multiple devices on the same bus.

Is 485 a half-duplex?

A simple RS-485 network consists of one master and up to 32 slave devices. Since RS-485 uses half-duplex communication—that is, the same two wires (D+ and D- shown below) are used for both transmission and reception—some means of controlling which side of the connection can transmit must be built into the system.

Is RS485 a protocol?

RS-485 is still the most widely used protocol for POS, industrial, and telecom applications. The wide common-mode range enables data transmission over longer cable lengths and in noisy environments such as the floor of a factory.

What is the use of RS485?

Is RS485 serial?

RS232, RS422, RS423, and RS485 are all essentially physical layer protocols. They are all serial communication protocols and are ubiquitous device interfaces.

Is Modbus full-duplex?

Although the Modbus over Serial Line specification supports both a 2-wire and 4-wire arrangement, the 2-wire implementation is the most popular. Although it is possible to have a full-duplex link with 4 wires, the Modbus protocol is strictly half- duplex.

What voltage is RS485?

Standard RS485 transceivers operate over a limited common mode voltage range that extends from –7V to 12V. In a commercial or industrial environment, ground faults, noise, and other electrical interference can induce common mode voltages that exceed these limits.

Does RS485 need termination?

Both ends must be terminated since the direction of propagation is bidirectional. In case of an RS485 twisted pair cable this termination is typically between 120 and 130 Ω. Here is a simple schematic of how the end of the lines should be terminated: “RT” is the 120 Ω termination resistor.

Can RS-485 and RS-422 be made full-duplex?

RS-485, like RS-422, can be made full-duplex by using four wires. Since RS-485 is a multi-point specification, however, this is not necessary or desirable in many cases. RS-485 and RS-422 can interoperate with certain restrictions.

How many RS-485 transceivers are there?

RS-485/RS-422 Transceivers. Maxim offers over 160 RS-485/RS-422 transceivers for applications such as automotive, HVAC, metering, and point of sale (POS). RS-485 transceivers are available in both industry-standard packages and small, spacing-saving packages.

What is the difference between RS422 and RS485?

RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422. It is generally accepted that RS-485 can be used with data rates up to 10 Mbit/s or, at lower speeds, distances up to 1,200 m (4,000 ft).

What is the difference between dh485 and RS485?

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. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units.