The equipment located along a set of RS-485 siemens tia portal v13 manual pdf are interchangeably called nodes, stations or devices. Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance.
Typical bias network together with termination. Biasing and termination values are not specified in the RS-485 standard. Without termination resistors, reflections of fast driver edges can cause data corruption. Termination resistors also reduce electrical noise sensitivity due to the lower impedance.
TIA” to help identify the origin of its standards. The EIA has officially disbanded and the standard is now maintained by the TIA as TIA-485, but engineers and applications guides continue to use the RS-485 designation. RS-485 only specifies electrical characteristics of the generator and the receiver. Other standards define the protocols for communication over an RS-485 link. These characteristics include: definition of a unit load, voltage ranges, open circuit voltages, thresholds, and transient tolerance.
The data is transmitted on “A” and “B”. C” is a ground reference. If A is negative with respect to B, the state is binary 1. The standard does not assign any logic function to the two states. Applying the bias at multiple node locations could possibly cause a violation of the RS-485 specification and cause communications to malfunction. Since RS-485 is a multi-point specification, however, this is not necessary in many cases.