串口线也分直连线和交叉线

- [ ] [如何区分直连串口线和交叉串口线？](https://blog.csdn.net/kevinhg/article/details/6930382)
- [ ] [DB9引脚在UART，CAN，RS485中的定义](https://www.cnblogs.com/legend-yuan/p/8082418.html)

Read the two linked reference articles about straight-through and crossover serial cables and DB9 pin definitions for UART, CAN, and RS485. Then inspect the blog's existing post structure and determine where this material belongs; done means the requested serial-cable and pin-definition content is published and the checklist item can be closed.

Written by the indexing model from the issue text.