Abstract: CANopen is a high-level communication protocol based on Controller Area Network (CAN). The object dictionary is the core concept in the protocol. Through thorough understanding of its related content, using CANOpen will be more than enough.
The CANopen object dictionary (OD: Object DicTIonary) is the core concept of the CANopen protocol. The so-called object dictionary is an ordered group of objects, describing all the parameters corresponding to the CANopen node, including the location of the communication data is also included in its index, this table becomes a transferable form called EDS file (Electronic Data file) Sheet) . The object dictionary, like the physical examination table, has the parameters of each function of the person, which is convenient for the employer (master station) to perform reasonable allocation work. As shown in Figure 1.
Figure 1 Object dictionary and medical examination form
Each object is addressed with a 16-bit index value, commonly referred to as an index, which ranges from 0x0000 to 0xFFFF. In order to avoid a large amount of data when there is no index to be allocated, an 8-bit index value is also defined under some indexes. This index value is usually called a sub-index, and its range is between 0x00 and 0xFF.
The specific parameters in each index are represented by a maximum of 32-bit variables, that is, Unsigned32, four bytes.
Each CANopen device has an object dictionary that uses electronic data files (EDS files) to record these parameters without having to record them on paper. For the master node in the CANopen network, there is no need to access every object dictionary entry for the CANopen slave node.
The items in the CANopen object dictionary are described by a series of sub-protocols. The sub-protocol describes each function in the object dictionary its function, name, index, sub-index, data type, and whether the object is required, read and write attributes, etc., so as to ensure compatibility of devices of the same type from different vendors.
The core description sub-protocol of the CANopen protocol is DS301, which includes the CANopen protocol application layer and communication structure description. Other protocol sub-protocols complement and extend the DS301 protocol description text. A CANopen device sub-protocol is drafted in different application industries. The sub-protocol number is generally DS4xx.
Object dictionary overview
As shown in Table 1, the object dictionary index area is defined, wherein the communication object sub-protocol area and the manufacturer-specific sub-protocol area marked with green shading are areas that the user needs to pay attention to.
Table 1 Object Dictionary Overview
Communication object sub-protocol area (CommunicaTIon profile area)
The communication object sub-protocol area (CommunicaTIon profile area) defines all communication-related object parameters. As shown in Table 2, the index range of the standard green shading is 1000h to 1029h, which is a universal communication object. All CANopen nodes must have these indexes. Otherwise you will not be able to join the CANopen network. Other indexes are assigned and defined based on actual conditions.
Table 2 Communication object sub-protocol area
General communication objects (General communicaTIon objects)
Since the universal communication object is very important, the NMT master station (CANopen master station) usually reads all or part of the index in the universal communication object of all slave stations at startup, so all common communication objects must be in the CANopen slave station. Implementation, the user must also be familiar with these index addresses and their meanings. as shown in Table 3.
Table 3 Universal Communication Objects
Manufacturer-specific sub-protocol (Manufacturer-specific Profile)
The object dictionary index 2000h to 5FFFh is a manufacturer-specific sub-protocol, and is usually application data storing the applied sub-protocol. The communication profile area described above is a communication parameter for storing these application data. For example, the XGate-COP10 slave module of Guangzhou Zhiyuan Electronics stipulates:
l RPDO communication parameters are stored in 1400h to 15FFh. The mapping parameters are stored in the 1600h to 17FFh data storage for 2000h after the vendor custom zone;
l The communication parameters of TPDO are stored in 1800h to 19FFh. The mapping parameters are stored in 1A00h to 1BFFh. After the data is stored for 2000h, the vendor-defined area.
For special functions not defined in the device sub-protocol, the manufacturer can also define object dictionary objects in this area according to requirements. Therefore, this area is not necessarily the same definition for the same object dictionary entries for different vendors.
Standardized device profile (Standardized profile area)
Standardized device sub-protocols that define objects in the object dictionary for different types of standard devices in various industries. At present, there are more than a dozen sub-protocols defined for different types of devices, such as DS401, DS402, DS406, etc., whose index values ​​range from 0x6000 to 0x9FFF. Again, this area does not necessarily have the same definition for the same object dictionary entry for different standardized device sub-protocols.
filter,cylinder,solenoid valve
Wuxi Trenty Machinery & Equipment Co., Ltd. , https://www.elec-inverter.com