VHDL 语言实现的串转并 SPI 等等

实现-The SPI bus is a 3 wire bus that in effect links a serial shift-- register between the　master　and the　slave . Typically both the-- master and slave have an 8 bit shift register so the combined-- register is 16 bits. When an SPI transfer takes place, the master and-- slave shift their shift registers 8 bits and thus exchange their 8-- bit register values.