说明：  本实验完成的是8位异步FIFO的设计，其中写时钟100MHz,读时钟为5MHz，其中RAM的深度为256。当写时钟脉冲上升沿到来时，判断写信号是有效，则写一个八位数据到RAM中；当读时钟脉冲上升沿到来时，判断读信号是有效，则从RAM中把一个八位数据读出来。当RAM中数据写满时产生一个满标志，不能再往RAM再写数据；当RAM中数据读空时产生一个空标志，不能再从RAM读出数据。
(In this study, completed the 8-bit asynchronous FIFO design, which write clock 100MHz, read clock is 5MHz, the depth of the RAM 256. When the rising edge of write clock pulse when writing the signal is valid, then write an eight-bit data to RAM when the rising edge of read clock pulse, the judge read the signal is valid, from eight bits of data in RAM to a read out. When RAM is full of data to generate a full mark, can not go down RAM write data when the RAM data read empty an empty sign, can not read data from RAM.)