In addition to the load wire, some registers have a clear wire which when high puts 0 into every flip-flop of the register. One register, PC, contains an increment wire which when set high adds 1 to the binary number contained in the register. Though this sounds like there would need to be an extra adder just for this register, it is relatively easy to build a register which does this; a full adder is not required, merely some AND gates to propagate the carry through the register's flip-flops. In Fig. 7.1.3 we show the block diagram for one of these "super registers."