SPI（Serial Peripheral Interface，串行外设接口）是Motorola公司提出的一种同步串行数据传输标准，是一种高速的，全双工，同步的通信总线，在很多器件中被广泛应用。

SPI相关缩写
SS: Slave Select，选中从设备，片选。
CKPOL (Clock Polarity) = CPOL = POL = Polarity = （时钟）极性

CKPHA (Clock Phase)　 = CPHA = PHA = Phase = （时钟）相位

SCK = SCLK = SCL = SPI的时钟（Serial Clock）

Edge = 边沿，即时钟电平变化的时刻，即上升沿(rising edge)或者下降沿(falling edge)。


对于一个时钟周期内，有两个edge，分别称为：
Leading edge = 前一个边沿 = 第一个边沿，对于开始电压是1，那么就是1变成0的时候，对于开始电压是0，那么就是0变成1的时候；
Trailing edge = 后一个边沿 = 第二个边沿，对于开始电压是1，那么就是0变成1的时候（即在第一次1变成0之后，才可能有后面的0变成1），对于开始电压是0，那么就是1变成0的时候；(SPI (Serial Peripheral Interface, serial peripheral interface) is a synchronous serial data transmission standard put forward by Motorola company, is a high-speed, full duplex, synchronous communication bus, is widely used in many devices.
SPI related abbreviations
SS: Slave Select, selected from the device, chip select.
CKPOL (Clock, Polarity) = CPOL = POL = Polarity = (clock) polarity
CKPHA (Clock, Phase) = CPHA = PHA = Phase = (clock) phase
SCK = SCLK = SCL = SPI clock (Serial, Clock)
Edge = edge, instant clock, level change time, i.e. rising edge (rising, edge) or falling edge (falling, edge).
For a clock cycle, there are two edge, respectively:
Leading edge = front edge = first edge, for start voltage is 1, then 1 is 0, for start voltage is 0, then 0 is 1;
Trailing = edge = second after an edge edge, the start voltage is 1, it is 0 to 1 of the time (that is, after the first 1 to 0, it may be behind the 0 to 1), the start voltage is 0, it is 1 to 0 times;)