0: the system clears it;
1: No processing.
Bit1: Execute user program in external
interrupt subroutine.
0: execute in task;
1: Execute in interrupt (in this mode, the user
interrupt subroutine cannot contain C
language function block). This mode is
generally used in occasions that require high
real-time performance of external signals.
Bit2: whether to raise the external interrupt
priority.
0: not raise;
1: raise (raise to the highest).