Sets an interrupt vector. Usage: JMP $E45C

||Register||Value
|X|MSB
|Y|LSB
|A|vector to be changed, see below

||Value||Vector
|0|[VIMMEDIRQ]
|1|[TIMCOUNT1]
|2|[TIMCOUNT2]
|3|[TIMCOUNT3]
|4|[TIMCOUNT4]
|5|[TIMCOUNT5]
|6|[VBLKIVKT]
|7|[VBLKDVKT]