I have in my box of parts a phototriac coupler, namely a Sharp PC3SD21NTZ (datasheet), which is a zero cross type. I don't know how to use it, but I've been meaning to learn for a while.
This part is specifically intended for triggering a main triac in load control applications and "are ideal isolated drivers for medium to high current triacs". Typical application from the datasheet:
When triggering the main triac directly, one would typically have a zero-cross detection circuit which a microcontroller can use as an input to decide when to trigger the triac. However, this part does not appear to offer any way for the microcontroller to detect zero crossing, which leaves me wondering what its purpose is in the first place.
What kind of input would one typically drive onto the diode side when using this part? Is it intended for on/off control only?