Описание тега rs485

RS-485 does not define a protocol; merely an electrical interface. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone.

RS-485 standard similar to rs232 but with an important addition, RS-485 uses a balanced line (an simple electrical method for rejecting inducted noise) which enables it to run either at higher speed or longer distance.

The RS-485 differential line consists of two pins:

• A, which is low for logic 1 and high for logic 0.
• B, which is high for logic 1 and low for logic 0.

https://stackru.com/images/7458a11af89bedee7ac43f0610784e846adbda84.png

In addition to the A and B connections, the EIA standard also specifies a third interconnection point called SC, which is the common signal reference ground. This connection may be used to limit the common-mode signal that can be impressed on the receiver inputs. This third signal is the reference potential used by the transceiver to measure the A and B voltages.

RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. This allows RS-485 to implement linear bus topologies using only two wires. The recommended arrangement of the wires is as a connected series of point-to-point (multidropped) nodes, i.e. a line or bus, not a star, ring, or multiply connected network.

More Information:

https://en.wikipedia.org/wiki/RS-485

Polarities for Differential Pair Signals RS-422 and RS-485

Guidelines for Proper Wiring of an RS-485 (TIA/EIA-485-A) Network