secondary principle schematics
或
secondary principle diagrams
参考资料：
有使用说明书和必要的电路图和原理图.
The instrument must be accompanied by instructions manual with the necessary schematics and drawings.
如果可能,掌握各个设备串口的原理图是很有用的.
If possible it is often useful to have a schematic of the serial port of each device in a system.
给出硬件接口电路原理图以及主程序软件流程图.
Gives the principle diagram of the hardware interface circuit and the software flow chart of the main program.