I'm working with a µcontroller whitout SPI port and I have to use a "Direct Digital Synthesizer" with a 3-wire serial interface. It's an Analog Device AD9833 which is written when the cheap select is low. I have chosen to use the UART interface from µC in a special mode :

clock on TxD
data on RxD

I miss a wire of cheap select and I think I can do it with a classical I/O pin from µC.

My question is about the synchronisation : Is the clock which manage the synchronisation or the cheap select ?

thanks
best regards
christophe.