RS485 Communication in Power Supply

RS485 is one of them, which has the following characteristics:

1. Using differential signals. The biggest advantage of differential input signals is that they can suppress common mode interference. Especially when the industrial environment is complex and there is a lot of interference, using differential methods can effectively improve communication reliability. RS485 uses two communication lines, usually represented by A and B or D+and D -. Logic "1" is represented by the voltage difference between two lines as+(0.2-6) V, while logic "0" is represented by the voltage difference between two lines as - (0.2-6) V. It is a typical differential communication.

Strictly speaking, all signals are actually differential signals because all voltages can only be relative to another voltage. But for most systems, we use the GND of the system as the reference point. For differential input, usually in addition to GND, there are two other input signals with the same amplitude and opposite polarity. In fact, it is easy to understand, just like a seesaw. As shown in the figure below.

If differential input is used, it is not a single input, but a group of inputs composed of two input terminals. PCF8591 is a total of

Four analog inputs can be configured into four modes, with the most typical being the two differential modes formed by four input terminals, such as

As shown in the figure below.

Four analog channels are configured as two differential mode inputs for channel 0 and channel 1. Taking channel 0 as an example, where AIR0 is the forward input and AIR1 is the reverse input, the signal inputs between them are signals with the same amplitude but opposite polarity. After passing through the subtractor, the difference between the two input channels is obtained, as shown in the figure below.

2. RS485 has a fast communication speed, with a maximum transmission speed of over 10Mb/s.

3. The internal physical structure of RS485 adopts a combination of balanced drivers and differential receivers, greatly enhancing its anti-interference ability.

4. The maximum transmission distance can reach about 1200 meters, but its transmission speed is inversely proportional to the transmission distance. Only at a transmission speed below 100Kb/s can the maximum communication distance be achieved. If further transmission distance is needed, a relay can be used.

5. Multi machine communication can be achieved through networking on the bus, and multiple transceivers are allowed to be mounted on the bus. From the existing RS485 chips, there are drivers that can be mounted on different devices such as 32, 64, 128, 256, etc.

6. The interface of RS485 is very simple, similar to the MAX232 used in RS232. With only one RS485 converter, it can be directly connected to the UART serial port of the microcontroller and use the same asynchronous serial communication protocol. However, due to RS485 being a differential communication, receiving and transmitting data cannot occur simultaneously, which means it is a half duplex communication.