Manufacturers supply LED lamp bead SMD LED 0805 yellow light super bright indicator light dedicated

Factory direct sales - solid capacitor - patch aluminum electrolysis, to ensure that the factory first-class goods!

1. Clarify several concept concepts: The communication distance of the 485 bus can reach 1200 meters.
In fact, only the 485 bus structure theoretically makes it possible to make the transmission distance reach 1200 meters under the premise of an ideal environment. Generally speaking, the communication wire quality is up to standard, the baud rate is 9600, only one 485 device can make the communication distance reach 1200 meters, and communication can not mean that every communication is normal. Therefore, the actual stable communication distance of the 485 bus is far less than 1200 meters. Load 485 equipment, wire impedance is not up to standard, wire diameter is too thin, converter quality is poor, equipment lightning protection, baud rate and other factors will reduce the communication distance.
Concept 2: The 485 bus can communicate with 128 devices.
In fact, not all 485 converters can carry 128 devices. It should be judged according to the model used in the chip in the 485 converter and the model used in the 485 device chip. Whoever is low is who. Generally, the 485 chip load capacity has three levels: 32 units, 128 units, and 256 units. The theoretical nominals are often not attainable. 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, the insufficient power supply of the converter (passive converter), the stronger the lightning protection, which will greatly reduce the real load. Quantity.
Concept 3: The 485 bus is the simplest, most stable and mature industrial bus structure.
This concept is wrong. It should be: The 485 bus is an economical traditional industrial bus method for device networking. Communication quality needs to be tested and debugged based on construction experience. Although the 485 bus is simple, it must be installed strictly in accordance with the construction specifications.
2. Strictly several construction specifications 485+ and 485-data lines must be twisted together.
The wiring must be covered with multiple shielded twisted pairs. The multiple strands are for standby. The shielding is for debugging in special situations. The twisting is because 485 communication adopts the principle of differential mode communication, and the twisting resistance is the best. Not using twisted pair is extremely wrong.
The 485 bus must be a hand-held bus structure that resolutely eliminates star connections and bifurcation connections. The AC power and chassis of the equipment must be grounded and grounded. There are many places where there are triangular sockets on the surface. In fact, there is no grounding at all. Be careful. When the grounding is good, you can ensure that the equipment is struck by lightning.
Surge impact, static electricity accumulation, can be combined with the lightning protection design of the device to release energy. Protect 485 bus devices and related chips from damage. Avoid walking with strong electricity to avoid interference from strong electricity.
3, several common communication faults are not communicated, no response. You can upload data, but you can't download data. When communicating, the system prompts interference. When the communication is not in progress, the communication indicator flashes continuously. Sometimes it can communicate, sometimes it can't communicate. Some commands can be passed, and some commands cannot be passed.
4. Recommend several debugging methods First, make sure that the equipment is wired correctly and strictly in accordance with the specifications.
Common ground method: Connect the GND ground of all 485 devices with 1 wire or shielded wire, so as to avoid the potential difference between all devices affecting communication.
Terminating resistor method: Connect the 120 ohm terminating resistor on the 485+ and 485- of the last 485 device to improve the communication quality.
Intermediate segmentation method: Check whether it is the device load is too large, the communication distance is too long, and the impact of a certain device on the entire communication line is caused by disconnection from the middle.
Single pull method: Pull a line to the device temporarily and easily, which can be used to eliminate whether the wiring is causing communication failure.
Replace the converter method: carry a few converters with you, which can eliminate whether the quality of the converter affects the communication quality.
Notebook debugging method: First ensure that the computer notebook that you carry with you is a normal communication device, replace the client computer to communicate, if it can, it indicates that the serial port of the customer's computer may be damaged or injured.
5. Suggestions and advice are recommended for users to use and purchase the 485 converter provided by the access control manufacturer or the 485 converter of the manufacturer's designated recommended brand. The access control manufacturer will do a lot of testing work with its associated 485 converter, and will separately require 485 manufacturers to install their fixed performance parameters for production and quality testing, so it has good compatibility with its access control equipment. Don't be tempted to buy a 485 converter from a brand-name manufacturer.
Construction in strict accordance with the construction specifications of the 485 bus, to prevent any luck.
Active scientific and reserved solutions are adopted for the case where the line has a long load.
If the communication distance is too long, it is recommended to use a repeater or 485HUB to solve the problem if it exceeds 500 meters. If there are too many loads, it is recommended to use 485HUB to solve the problem if there are more than 30 on one bus.
On-site commissioning with debugging equipment.
On-site commissioning must carry a few converters that ensure long distances and multiple loads, a common computer notebook, a multimeter with a test path open circuit, and several 120 ohm terminating resistors.