== Control Registers ==
* 8253 /8254 Timer 0-2 Control Registers (W)
This port allows to configure three write-only 6bit registers: Bit6-7 specify which of the registers is to be updated, Bit0-5 contain the new value for that register.
7-6 Counter Number (0..2=Counter 0..2, and 8253: 3=Reserved, or 8254: 3=Readback)
5-4 Read/Load (0=Latching?, 1=LSB only, 2=MSB only, 3=LSB-then-MSB)
3-1 Mode