What Is the SPI Interface?
SPI (serial peripheral interface) is an interface standard defined by Motorola on the MC68HCxx line of microcontrollers. A synchronous clock shifts serial data into, and out of, the microcontrollers in blocks of 8 bits. Whenever two devices communicate, one is referred to as the “master” and the other as the “slave” device. The master drives the serial clock. When using SPI, data is simultaneously transmitted and received, making it a full-duplexed protocol. The 68HC11 allows four configurations of SPI, which are designated by CPOL and CPHA: • When CPOL = 0, the clock idle state is low. • When CPOL = 1, the clock idle state is high. • When CPHA = 0, the first clock edge clocks data into and out of the microprocessor. If CPOL = CPHA, then the rising edge clocks data into and out of the microprocessor. • When CPHA = 1, the second clock edge clocks data into and out of the microprocessor. If CPOL does not equal CPHA, then the falling edge clocks data into and out of the microprocessor. Mo
