RS485 solution
1、 Several concepts about 485 bus:
According to the theory of 485 bus structure, the transmission distance of 485 bus can reach 1200 meters under the premise of ideal environment.
The condition is that the baud rate of the communication wire is 9600, and only one 485 device can make the communication distance reach 1200 meters. Therefore, the actual stable communication distance of 485 bus is often less than 1200 meters. If there are many load 485 devices, the wire impedance does not meet the standard, the wire diameter is too thin, the converter quality is poor, the lightning protection of the equipment is complex, and the baud rate is increased
Higher and other factors will reduce the communication distance.
In fact, not all 485 converters can carry 128 devices, which depends on the model and
485 device chip model only the chip with lower index can determine its load capacity. General 485 chip
There are three levels of load capacity - 32, 128 and 256.. In addition, the nominal in theory is often actually up to
Less, the longer the communication distance, the higher the baud rate, the thinner the wire diameter, the worse the wire quality, the worse the converter quality, and
Insufficient power supply (passive converter) and stronger lightning protection will reduce the number of real loads.
3. 485 bus is the simplest, most stable and most mature industrial bus structure
485 bus is an economical and traditional industrial bus mode used for equipment networking.
Its communication quality needs to be debugged and tested according to construction experience, which can be guaranteed. Although 485 bus is simple, it must be wired in strict accordance with the installation and construction specifications.
During the construction of 485 bus system, the construction must be carried out in strict accordance with the construction specifications. In particular, you should pay attention to the following points:
1. 485+ and 485 data lines must be twisted to each other and close together.
2. Multi strand shielded twisted pair must be laid for wiring. Multi strand is for standby, which is convenient for debugging in case of special circumstances. Twisted pair is because 485 communication adopts the principle of differential mode communication, and twisted pair has good anti-interference performance. It is wrong to separate the positive and negative lines, which is easy to cause error code.
3. 485 bus must use hand-in-hand bus structure, and resolutely avoid star connection and bifurcation connection.
In fact, there is no grounding at all. A good grounding can prevent the equipment from being struck by lightning and surge. It can be set when static electricity accumulates
The lightning protection design of the equipment can better release energy to protect 485 bus equipment and related chips from damage.
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