RS-485 and RS-422 are both serial communication standards that share similarities but have distinct differences in terms of their electrical characteristics and intended applications. Here's a comparison between RS-485 and RS-422 communication:

1. Number of Drivers and Receivers:

   • RS-485: Supports multiple drivers and receivers on the same communication bus, enabling multi-point or multi-drop communication. It allows one driver to communicate with multiple receivers.
   • RS-422: Supports only one driver and up to ten receivers on a point-to-point communication link. It does not support multi-drop configurations.

2. Signal Lines:

   • RS-485: Uses two signal lines for data transmission (A and B), along with a common ground reference (GND). It employs balanced differential signaling, where the voltage difference between A and B represents the transmitted data.
   • RS-422: Also uses two signal lines for data transmission (Tx+ and Tx- for transmission, Rx+ and Rx- for reception), along with a common ground reference (GND). Like RS-485, it utilizes balanced differential signaling.

3. Voltage Levels:

   • RS-485: Supports differential voltage levels, typically ranging from -7V to +7V or -5V to +5V. This allows for greater noise immunity and longer communication distances.
   • RS-422: Also supports differential voltage levels, typically ranging from -5V to +5V. It provides good noise immunity but is generally limited to shorter communication distances compared to RS-485.

4. Communication Distance:

   • RS-485: Designed for longer communication distances, typically up to 1200 meters (about 4000 feet) at lower data rates and several hundred meters at higher data rates.
   • RS-422: Supports shorter communication distances compared to RS-485, typically up to 1200 meters (about 4000 feet) at lower data rates and shorter distances at higher data rates.

5. Termination and Biasing:

   • RS-485: Requires termination resistors at each end of the communication bus to minimize signal reflections and impedance matching. It may also require biasing resistors to set the idle state of the bus.
   • RS-422: Often does not require termination resistors due to its point-to-point nature. However, termination may be necessary in certain high-speed or long-distance applications.

6. Applications:

   • RS-485: Widely used in industrial automation, process control, building automation, and other applications requiring long-distance communication and multi-point configurations.
   • RS-422: Commonly used in point-to-point communication links, such as connecting a computer to a peripheral device, or for communication between two pieces of equipment over a short distance.

In summary, RS-485 is designed for multi-point communication over long distances, while RS-422 is primarily intended for point-to-point communication over shorter distances. Both standards utilize balanced differential signaling for improved noise immunity and reliability.