Clock Source operation: A user can add a clock source or clear a clock source. After a user adds a clock source,the clock works in trace mode. After a user clears a clock source, the clock works in srystal mode. To set the position(frame,slot,port) and oper(4), these two operations must be set together. Oper(6) can be set by itself. To set a BITS clock source, the frame,slot,port parameters are useless. Oper(6) is used to clear a clock source.