How Does SPI Determine the Starting Point of Data Transmission?

[themagiciant95]

I have a SPI with a master and a slave:

How the system knows what's the starting point of the data sent ? It's ok that we have the clock, but both MOSI and MISO have a default state on "1", that may be sampled as data sent

 

[Tom.G]

The Clock signal runs only when there is a byte to transmit.

See page 8, section 1.3.5.1
http://www.ti.com/lit/ug/slau411e/slau411e.pdf

 

[themagiciant95]

Thanks. When i studied the UART protocol i read that it need a common ground:

In the SPI diagram it doesn't appear. Why ? Probably i don't clearly understand what a commond groud is... :(

 

[anorlunda]

In the SPI diagram it doesn't appear. Why ?

It is just implicit. They didn't bother to put it in the diagram, but it's there.