实现FPGA 按键控制部分代码，FPGA芯片采用xilinx sptan3e 可以实现按下按键后FPGA通过max232给电脑发送数据-Achieve FPGA button control part of the code, the FPGA chip using xilinx sptan3e can realize after press the button the FPGA through max232 send data to a computer