TI中文支持网1.参考里边说SPI有三线模式，是说CS管脚不用接吗？
2.还有就是看到这么句话，红色背景标出来的，是说CS脚必须链接吗
Transmit Enable
The TALK bit can disable data transmission (master or slave) by
placing the serial data output in the high-impedance state. If this bit
is disabled during a transmission, the transmit shift register
continues to operate until the previous character is shifted out. When
the TALK bit is disabled, the SPI is still able to receive characters
and update the status flags. TALK is cleared (disabled) by a system
reset.
0h (R/W) = Disables transmission:
– Slave mode operation: If not previously configured as a generalpurpose
I/O pin, the SPISOMI pin will be put in the high-impedance
state.
– Master mode operation: If not previously configured as a generalpurpose
I/O pin, the SPISIMO pin will be put in the high-impedance
state.
1h (R/W) = Enables transmission For the 4-pin option, ensure to
enable the receiver's SPISTEn input pin.
answer：
三线模式时，不会用到CS引脚，如果需要用到4线模式，CS必须连接
