When BPINT is keyed with an interrupt-number greater
than 5FH, the error message "invalid interrupt number" is
The Windows IDT only handles interrupts 00 to 5F;
interrupts above this are dispatched through general protection
faults. To set a breakpoint on a higher interrupt, get the real
mode interrupt vector, and set a BPX on the first instruction in
the real mode interrupt service routine.