Detailed explanation of BACnet protocol - preface

After thinking for a long time, I finally made up my mind to write a column about BACnet on the last working day of 2022. In the automatic building industry, the BACnet protocol should be a mountain that most engineers cannot get around. BACnet, the abbreviation of Building Automation and Control networks, is the building automation and control network. In other words, BACnet is designed for building automation control, so if you are in the building automation control industry, then you must understand this protocol, or you must master this protocol. The BACnet protocol is an American standard protocol, but most of the mainstream products are based on this protocol, such as Siemens, Johnson, Honey and other companies. So far, all the projects I participated in have been applied to the BACnet protocol, and I have been deeply involved in the porting and use of the BACnet protocol stack. At the same time, when working on these projects, because we bought a commercial protocol stack and encountered problems in use, we were also fortunate to have some exchanges with the makers of the BACnet protocol, and when these people explained, they Instead of simply telling you the solution to this problem, I will tell you about the past and present of this problem and the similar problems encountered by other people, so communicating with them is really beneficial. In each of these projects, from first knowledge to understanding and then to in-depth understanding, I gradually have a certain understanding of BACnet. In the process of applying it slowly, I realized the power of BACnet more and more, and my understanding of BACnet became deeper and deeper. Therefore, my suggestion to engineers who are interested in BACnet who read this column is that whether you read this column or read the agreement, you are talking on paper, and your understanding of BACnet is only in the literal meaning. Only when you use all objects and services in your project, can you gradually have a deeper understanding of the design of the entire object or service. Just like when I was doing trend log object for the first time, I read the protocol of trend log object and related services, and finally found that the implementation method could not pass the BTL test due to lack of understanding. Therefore, I want to share some of my understanding and the pitfalls I have waded through in the past. One is as a record for future reading, and the other is to communicate with everyone, so that everyone can make progress together!
Written in the back, it is expected to update a blog about BACnet every two weeks in 2023, which can not only ensure the quality of the blog, but also give everyone a time to communicate and learn. The previous blogs should be more about writing the original English version of the agreement in your own words. Because the previous chapters involved some architecture, application layer, network layer, and things related to the MAC protocol, which are basically fixed things. Of course, there must be some personal understanding in it, especially in my project. Corresponding descriptions of some of the problems encountered in . But the most comprehensible explanations are still in the part of object and service, because the property of this part of object will have some linkage with service, so I will break the typesetting of the original agreement and combine object with some related services, so that It will be easier for us to understand the BACnet protocol.