说明：  在制作ARM的开发板时，其中的JTAG接口有20针以及14针的，先上传文档说明他们的区别及引脚排列，希望对大家有所帮助！
(In the production of ARM development board, one of the JTAG interface has 20-pin and 14 pin, first upload document explains the difference between them and pin arrangement, and they hope to be helpful to everyone!)