When an instruction starts, some one RCL will see its own address on the top 8 bits of the instruction word and its iAmSource will go high. If copy start is also true and its backend device is also readReady, it will set EN-OUT, which puts all its register's 32 bits onto the data bus. And then it generates copy in progress.

Now let us look at what happens when the source's backend readReady is NOT set.

For example, let's say that our backend device is a simple on/off toggle switch whose readReady goes high whenever the switch is flipped, and low again after the register is read. Thus its quiescent state is low, that is, not ready. It might stay in that state for years, until someone flips that switch.

If an instruction starts that reads this register, iAmSource goes high, copy start is high, but readReady is low. The top 3-input AND's output is low. Enable output stays low and copyInProgress is not set.

       *** AND EVERYTHING STOPS! ***

As a sequential circuit, no signal propagates beyond this point. As copyInProgress is not asserted the destination register will also block at its bottom 3-input AND.

Thus the entire WIZ Frontend circuit is frozen.

In CMOS, no movement means no power is being used. Of course, the backend circuits may be doing lots of computing. And in a chip of many WIZes, all other WIZes may be running.

But until somebody flips that external switch, on this one WIZ's Frontend, nothing happens. It may take a century before that switch is flipped, and our WIZ will just sit there, consuming no power, "waiting" for it.

In a clocked system, the clock would keep flipping, driving a huge capacitive load and flipping thousands of attached transistors across the entire circuit. Some systems apply "clock gating" to shut off the clock in non-active areas, or have special "sleep" modes, but this has a very large granularity. On a WIZ chip, each WIZ is individually active, or not.

(A fun -- and somehow related -- fact: A typical microwave oven consumes more power to run its clock than to microwave food! Because while microwaving food takes hundreds of times more power on an instantaneous basis, most microwave ovens sit idle most of the time, while their clocks continue to run all the time!)