这里详细介绍了CAN协议中数据通信帧每位的含义，有图片，值得一看：https://www.cnblogs.com/pejoicen/p/3986587.html
这里介绍了CanOpen协议，https://blog.csdn.net/plc_jianghao/article/details/77824241
再看官网解释：https://www.can-cia.org/can-knowledge/canopen/sdo-protocol/
CanOpen开源项目：
项目名：CANopenSocket
项目地址：https://github.com/CANopenNode/CANopenSocket
项目介绍：
CANopenSocket is a collection of CANopen tools running on Linux with socketCAN interface.
CANopenSocket consists of two applications: canopend, which runs in background, and canopencomm, command interface for SDO and NMT master.
canopend
canopend is an implementation of CANopen device with master functionality. It runs within three threads. Realtime thread processes CANopen SYNC and PDO objects. Mainline thread processes other non time critical objects. Both are nonblocking. Command interface thread is blocking. It accepts commands from socket connection from external application and executes master SDO and NMT tasks.
canopencomm
canopencomm is the other end of the Command interface. It accepts text commands form arguments or from standard input or from file. It sends commands to canopend via socket, line after line. Received result is printed to standard output. It is implementation of the CiA 309 standard.