VHDL實現SPI功能源代碼
-- 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.
