RS232485

RS232 and RS485 are two widely used serial communication standards defined by the EIA/TIA family. They address different signaling methods, topologies, and applications. In practice, devices may include interfaces for RS-232 or RS-485, or use converters to bridge between them.

RS-232 is a single-ended, point-to-point standard designed for asynchronous data transmission between two devices, such as a computer and a modem. It uses individual signal lines and a common ground. Logic levels are represented by voltage ranges where a mark is typically negative and a space is typically positive, with common practice voltages in the range of a few volts to tens of volts. RS-232 supports simple, low-cost interfaces but is limited in distance and wiring complexity; practical cable lengths are relatively short at higher speeds. Typical implementations use 9- or 25-pin connectors. The standard is well suited for direct connections over short runs but does not tolerate long cables or multi-point networks without repeaters or level shifting.

RS-485, by contrast, uses differential signaling on twisted-pair conductors to enable robust communications over longer distances and in electrically noisy environments. It supports multipoint networks, with multiple drivers and receivers on the same bus. RS-485 can operate in half-duplex (two-wire) or full-duplex (four-wire) configurations. A typical RS-485 network uses termination resistors at each end of the bus and biasing resistors to establish an idle state. Distances can exceed a kilometer at lower data rates, while higher speeds are achievable over shorter runs. RS-485 is commonly used in industrial control and automation networks, such as Modbus RTU.

In practical systems, RS-232 and RS-485 may be connected via protocol converters or transceivers that adapt signals between the two standards.