A, RS485 bus Introduction RS485 bus is a common serial bus standard, using balanced differential transmit and receive mode, and therefore has the ability to suppress common mod
e interference. In some of the requirements on the communication distance of tens of meters to kilometers when, RS485 bus is a bus most widely used. But also in the operation of the system of multi-node also has a wide range of applications. Two, RS485 bus describes a typical circuit It can be divided into isolated and non-isolated RS485 circuit as a whole. Isolated than non-isolated in interference, system stability and other aspects of better performance, but there are some situations you can also use non-isolated. We speak about non-typical circuit isolated and non-isolated circuit is very simple, just a RS485 chip directly with MCU serial communication port and an I/O control port connection can be. As shown in Figure 1: in line B plus a pull-down bias resistors of 4.7K. Matching resistor R16 is in the middle, typically 120, of course, this depends on your specific transmission cables. (Matching resistor: 485 entire communication system for transmission system stability, we will normally be the first node and last node plus matching resistance so we are generally in the design, you will have a set at each node jumper 120 resistance, as to use or not, by the field staff to set. of course, specifically how to distinguish between the first node is the last node, have to be on-site experts to answer Oh.) TVS we generally use 6.8V and this we will further explain later.