The basic principle of CAN communication in the weighing instrument table
CAN (Cantroller Area Network) system bus, that is, control panel local area network system bus, has been widely used in industrial control systems, electrical products and sensor industries. The CAN bus protocol has two national standards, namely ISO11898 and ISO011519. Among them, ISO11898 is a high-speed communication specification, and the communication speed is 125kbps ~ 1Mbps; the larger communication distance is 40m/1Mbps, which belongs to the closed-loop control system bus. ISO011519 is a low-speed communication specification, the communication speed is 10kbps ~ 125kbps. The larger communication distance is 1Km/40kbps, which belongs to the open-loop transfer weighing instrument function system bus. Because the contact resistance and resistor of the system bus are harmful to the waveform of the system bus, the larger number of connection points on the CAN bus is 110. If the receiving and sending end serial port baud rate and main parameters are properly equipped, the database synchronization of the receiving and sending points can be completed. The data weighing instrument can be transmitted by several methods such as point-to-point, point-to-point, and global broadcast programs. When there is a connection point on the CAN bus to transmit data, it is sent to all connection points in the Internet in a message format. For each connection point, regardless of whether the data information is sent to itself or not, it will be accepted. The 11-bit identifier at the beginning of each group of message formats is the identifier, which defines the priority of the message format. The message format identifier in the same system software is unique, otherwise the communication will be wrong; the actual whole process is as follows: When a station wants to transmit data to another station, the CPU of the station transmits the data information and its own identifier. The CAN integrated ic of this website is in the pre-preparation situation; when it receives the system bus assignment, it becomes the push message format situation. The CAN integrated ic sends the data message weighing instrument information to the system bus in a certain message format according to the agreement. At this time, other stations on the system bus are in the receiving state, and each station in the receiving state responds to the received The message format is checked, and if it is sent to itself, data information analysis is carried out on it. What if there is a lot of additional data to be transmitted when the system bus is free? The first message format to be pushed separately is accepted and distinguished. Whoever has the highest priority will occupy the system bus, and the others will be discarded. For example: station 1, station 2, and station 3 additionally push the message formats to the system bus: 011111, 0100110, 0100111; the system bus will distinguish the message format, the first two bits are the same, and then the third bit is distinguished. 1 The third digit is 1, and the message format will be abandoned. Only station 2 and station 3 are left. The first six digits of these two stations are the same. The seventh digit of station 3 is 1, which will also be abandoned. The message format of station 2 is saved, and other stations are in the receiving situation, and it is not easy to push the message format before the system bus becomes free again. This is the incentive mechanism of the CAN communication system bus weighing instrument;