Typically, I think, a zero-crossing triac driver is for simple on-off stuff.So, maybe you're asking:if the input got pulsed, say at line peak (90deg or 270deg), would the driver side sit "armed", as a latch, primed, ready for zero-cross, where it would turn the triac on? Is that it?The triac can be triggered ON at any part of the sine wave except a actual zero crossing +/- a little, but a triac (or scr) can only be turned OFF at zero crossing AND an absent of a trigger signal. Most solid state AC relays allow internal turn ON only at zero crossing by design not because it can't be done. Those SSRs that have 'random' or 'proportional' turn on capabilities can switch on anytime in the AC cycle and are used for PWM applications rather then the slower on/off type control that most standard AC SSRs use.LeftyI'm not sure the form of the zero-crossing circuitry (internal). I haven't used one where half-cycles was an issue.