Sorry about the late reply. Our server was down on Oct 24 due to power failure caused by hurricane Wilma hitting Florida. The server came back on briefly on Oct 25 after the backup generator was repaired but at 1:10pm EST the backup generator failed again so the server is down whole day.
Anyway, regarding your questions, the interrupt edge means whether it is from OFF to ON (rising edge) or from ON to OFF (falling edge).
While the interrupt service custom function is run, the stepper output generator will continue to generate pulses. It will not be hindered by the interrupt custom function.