CONTROL REGISTER B:

  BIT  NAME     FUNCTION
  ---  ----     --------
   0   START    1 = start Timer B, 0 = stop Timer B.
                    This bit is automatically reset (= 0) when
                    underflow occurs during one-shot mode.
   1   PBON     1 = Timer B output on PB7, 0 = PB7 is normal
                    operation.
   2   OUTMODE  1 = toggle, 0 = pulse.
   3   RUNMODE  1 = one-shot mode, 0 = continuous mode.
   4   LOAD     1 = force load (this is a strobe input, there is no
                    data storage;  bit 4 will always read back a
                    zero and writing a 0 has no effect.)
  6,5  INMODE   Bits CRB6 and CRB5 select one of four possible
                input modes for Timer B, as follows:

                CRB6  CRB5   Mode Selected
                ----  ----   ---------------------------------------
                 0     0     Timer B counts 02 pulses
                 0     1     Timer B counts positive CNT transitions
                 1     0     Timer B counts Timer A underflow pulses
                 1     1     Timer B counts Timer A underflow pulses
                               while CNT pin is held high.

   7   ALARM     1 = writing to TOD registers sets Alarm
                 0 = writing to TOD registers sets TOD clock.
                     Reading TOD registers always reads TOD clock,
                     regardless of the state of the Alarm bit.