SPI中的几个概念

1、SPI通常涉及到的几个标准：

❐ Motorola SPI ： modes 0, 1, 2, and 3，最原始的SPI协议
❐ Texas Instruments SPI： with coinciding and preceding data frame indicator - mode 1 only
❐ National Semiconductor (MicroWire) SPI -  mode 0 only，半双工的变种

2、SPI中四线接口定义：

■ SCLK: Serial clock (clock output from the master, input to the slave).
■ MOSI: Master-out-slave-in (data output from the master, input to the slave).
■ MISO: Master-in-slave-out (data input to the master, output from the slave).
■ SELECT: Typically an active low signal (output from the master, input to the slave).

3、Motorola SPI中的四种时钟模式（极性CPOL和相位CPHA）

■ Mode 0: SCB_SPI_CTRL.CPOL is '0', SCB_SPI_CTRL.CPHA is '0': 
Data is driven on a falling edge of SCLK. Data is captured on a rising edge of SCLK. SCLK idle state is '0'.
■ Mode 1; SCB_SPI_CTRL.C