Confusion with edge-triggered D-type flip-flop in code by Charles Petzold

Question

I am confused about a circuit which is presented in Charles' Petzold's 'Code' book (Page 178), and I would like some clarification. The book says that the following flip-flop is edge-triggered:

I don't think this is the case unless I'm really stupid, but I hope that isn't the case.

The book does provide, earlier in the book, an example which I fully understand (Page 171):

In the example I am confused about it seems that it is level-triggered because after Clock is set to 1, Data still holds the ability to change the value of Q, as Clock does not control the flow of Data when it is both on and off; only when it is off does it prevent Data from making an impact, making it level-triggered, I believe.

The correct example I show only lets Data have an impact when Clock goes to 1, as there are two layers, and when Data flows to Q, Clock must be set to 0 in order for the data that will be sent to the second layer to be set, so I do understand that.

The two flip-flops, I am certain in saying, are inherently different due to the difference in the number of layers, and if an edge-triggered flip-flop can be made with one layer, why hasn't it been presented as an example instead?

Basically, am I right in this? I would like clarification from somebody who may understand it better. Is the book correct?

Answer 1

It might helpful to play with this Falstad simulation:

Falstad simulation

Here Clear and Preset are assumed to be 0.

The outputs X, Y, Z, W have the following values as functions of Q, Qn, CLK and D:

Q  Qn  CLK  X  Y  Z  W
1  0   0    D  0  0  /D    D changes only X and W
1  0   1    1  0  1  0     D has no effect
0  1   0    D  0  0  /D    D changes only X and W
0  1   1    0  1  0  /D    D changes only W

The important point is that toggling D does not affect the outputs Y and Z which are the Set and Reset signals for the output RS-flip flop.