I suspect he's figured out how he can do it. After all, if all he wants is to generate an interrupt, well, that's "do-able". Precise synchronization is a bit trickier, though. He doesn't have to use the receive interrupt, BTW. He could interrupt on the start bit, since the message is apparently irrelevant. I'm puzzled, in fact, by the notion that he wants to use the serial port at all if he has only a single function to perform with this feature.

You're right ... he needs to tell us more. I suspect his problem is less complex than was initially imagined.

As for the absolute synchronization ... if his RESET circuit is a sequencer, e.g. a 24-count state machine, triggered by the rising edge of RESET, and both slaves are sent the same RESET strobe, and both MCU's are clocked from the same master clock, perhaps held in synchronization with a PLL that's driven by the same lower-frequency originating at the master, he might be able to achieve absolute synchronization. It seems like a lot of trouble, though.

RE