RS-422 and RS-485 are both serial communication standards defined by the Electronic Industries Association (EIA). While they share similarities, they have distinct differences in terms of their electrical characteristics, capabilities, and applications. Here are the key differences between RS-422 and RS-485:

RS-422:

1. Point-to-Point Communication: RS-422 is primarily designed for point-to-point communication between two devices. It supports a single transmitter and multiple receivers but does not allow for multi-point or multidrop configurations.

2. Voltage Levels: RS-422 uses differential signaling, which means that data is transmitted as voltage differences between two signal wires (A and B). The voltage levels typically range from -6V to +6V, with a minimum voltage difference of 2V between the two signal wires.

3. Transmission Distance: RS-422 supports longer transmission distances compared to RS-232, typically up to 1200 meters (4000 feet) at lower data rates. It is suitable for applications requiring communication over longer distances without signal degradation.

4. Data Rates: RS-422 supports higher data rates compared to RS-232, typically up to 10 Mbps (megabits per second). It is commonly used in applications requiring high-speed data transmission, such as industrial automation, process control, and telecommunications.

5. Noise Immunity: RS-422 provides better noise immunity and signal integrity compared to RS-232, thanks to its differential signaling scheme. It is less susceptible to electromagnetic interference (EMI) and noise, making it suitable for use in electrically noisy environments.

RS-485:

1. Multi-Point Communication: RS-485 supports multi-point or multidrop communication, allowing multiple devices to be connected to the same bus or communication line. It supports multiple transmitters and receivers on the same bus, enabling communication between multiple devices.

2. Voltage Levels: Like RS-422, RS-485 also uses differential signaling, with voltage levels typically ranging from -6V to +6V. However, RS-485 allows for greater flexibility in voltage levels and signal levels, making it suitable for a wider range of applications.

3. Transmission Distance: RS-485 supports longer transmission distances compared to RS-422, typically up to 1200 meters (4000 feet) or more at lower data rates. It is commonly used in applications requiring communication over long distances, such as industrial automation, building automation, and remote monitoring systems.

4. Data Rates: RS-485 supports data rates similar to RS-422, typically up to 10 Mbps. However, the actual data rate may vary depending on factors such as cable length, signal quality, and environmental conditions.

5. Half-Duplex and Full-Duplex: RS-485 supports both half-duplex and full-duplex communication modes. In half-duplex mode, devices on the bus can transmit and receive data, but not simultaneously. In full-duplex mode, devices can transmit and receive data simultaneously, allowing for faster communication.

In summary, RS-422 and RS-485 are both serial communication standards that use differential signaling for robust and reliable communication. RS-422 is primarily used for point-to-point communication over longer distances, while RS-485 is used for multi-point communication over longer distances and in electrically noisy environments. The choice between RS-422 and RS-485 depends on factors such as transmission distance, number of devices, data rates, and environmental conditions.