means for providing {TAIL ~ clock pulses} for {HEAD ~ operation} of said shift register in read/write operations 
means for providing { TAIL ~ clock pulses } for { HEAD ~ operation } of said shift register in read / write operations
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH