This is accomplished by subtracting the contents of the B register from the contents of the A register and storing {HEAD ~ the result} in {TAIL ~ the B register} while forcing the A input of the ALU equal to zero 
in
This is accomplished by subtracting the contents of the B register from the contents of the A register and storing { HEAD ~ the result } in { TAIL ~ the B register } while forcing the A input of the ALU equal to zero
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH