sherzaad:
what I want, is the PC to know that an eStop has happened the moment it does; by that I mean if while the arduino it is transfering data to the PC an eStop happens, it "immediately" informs the PC... not go through the rest of the loop transferring whatever remaining (no longer invalid) data then tell the PC about the eStop conditon...
You need to explain why that level of immediacy is important.
...R