This object controls the type of clock used
as the source for the bus line.
If 'notConfigured', then this source isn't
configured.
If 'receiveDataDerived' then the source of
the clock comes from the specified port's
receive data (e.g. calculated using a Phase
Lock loop off the receive data line).
If 'onboardOscillator' then the source of
the clock comes from the on-board oscillator
associated with this port. Currently (as of
release 3.2) this is only valid with 19.44 Mhz
clocking, and not valid for 8 Khz clocking.