i am giving u general idea because in tch,sdcch and ccch configuration u need not to think about no of frequencies.
Frquency will come in picture when u will put that trx in hopping or non hopping mode.
now there is 2 mode for control channel configuration:
As ur BCCh will be on 0th timeslot and other 7 timeslot will be TCH.
so here ur sdcch will be also on 0th timeslot with bcch+sdcch/4 mode.so it will share the timeslot 0 with bcch.
2)now in noncombined mode ur sddch will be on 1st timelsot and bcch will be on 0th timeslot and other 6 timeslot will be on tch.
so here bcch+sdcch/8 configuration will be made.
so here u dont need to worry about freq.
if still any doubt then tell me.