McBSP in multichannel mode

I got with some doubts about the operation
of the McBSP serial port in the multichannel
configuration. The manual says tha it's possible
to acces up to 128 chanells on witch McBSP channel...
but it did not get clear for me.
Does anybody could give some hint about the operation of
the McBSP in multichannel mode (if possible with some example
 of application),and how the properly selection
of each channel could be achieved?
Thanks a lot...