16 bit timer
- Default base address is 0420h
- Can launch two interrupts:
- Timer tick (at Ftick = Fclk / prescaler [Hz])
- Timer counter compare (at Fcmp = Ftick / compare [Hz])
- Counter (at 0420h)
- incremented at Ftick [Hz]
- Prescaler (at 0421h)
- Enable register (at 0422h)
- bit 1: Timer enable
- Counter compare (at 0423h)
- if 0, counter compare is disabled