串口3接收，串口1、2發(fā)送。

Your Licence to Use the Source Code and Specification for the Cortex Microcontroller Software Interface Standard：

THIS END USER LICENCE AGREEMENT IS A LEGAL AGREEMENT （“LICENCE”） BETWEEN YOU （EITHER A SINGLE INDIVIDUAL， OR SINGLE LEGAL ENTITY） AND ARM LIMITED （“ARM”） FOR THE USE OF THE SOURCE CODE AND SPECIFICATION ACCOMPANYING THIS LICENCE. ARM IS ONLY WILLING TO LICENSE THE SOURCE CODE AND SPECIFICATION TO YOU ON CONDITION THAT YOU ACCEPT ALL OF THE TERMS IN THIS LICENCE. BY CLICKING “I AGREE” OR BY INSTALLING OR OTHERWISE USING OR COPYING EITHER OR BOTH THE SOURCE CODE AND SPECIFICATION YOU INDICATE THAT YOU AGREE TO BE BOUND BY ALL THE TERMS OF THIS LICENCE. IF YOU DO NOT AGREE TO THE TERMS OF THIS LICENCE， ARM IS UNWILLING TO LICENSE THE SOURCE CODE AND SPECIFICATION TO YOU AND YOU MAY NOT INSTALL， USE OR COPY THE SOURCE CODE OR SPECIFICATION， BUT YOU SHOULD PROMPTLY RETURN THE SOURCE CODE AND SPECIFICATION TO ARM.