说明：  本程序使用MSP430F149驱动PS2接口的PC键盘，使用了SN74LVC4245用作电平转换；PS2 端口使用了标准的六芯插座，可以接收来自标准键盘、鼠标的数据。由于键盘、鼠标都是 5V 供电系统，而 MSP430F149 只能工作在 3.3V，所以需要在两者之间进行电平转换。根据键盘的工作原理，MCU只要接收键盘发送过来的时钟信号和数据信号，然后对数据信号进行解码就可以了。为此我们利用了电平转换电路的两根数据线，让键盘的时钟线 CLK 连接SN74LVC4245 的A8 端口，键盘的数据线DATA连接SN74LVC4245 的A7 端口
(This procedure using the MSP430F149 the PC interface driver PS2 keyboard, used for SN74LVC4245 level conversion PS2 port using a standard six-core socket, you can receive from the standard keyboard and mouse data. As the keyboard, mouse are 5V power supply system, while the MSP430F149 can only work in 3.3V, so it is necessary to carry out between the two-level conversion. According to the working principle of the keyboard, MCU as long as the receiver from the keyboard to send the clock signal and data signals, data signals and then decode it. To this end, we made use of level-shifting circuit of two data lines, so that the keyboard clock line CLK of the A8 connection SN74LVC4245 port, keyboard data line DATA port to connect SN74LVC4245 the A7)