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The section of the textbook Digital Design by Morris M. Mano and Michael D. Ciletti says the following about D flip-flops:

Another construction of an edge-triggered D flip-flop uses three SR latches as shown in Fig. 5.10. Two latches respond to the external D (data) and Clk (clock) inputs. The third latch provides the outputs for the flip-flop. The S and R inputs of the output latch are maintained at the logic-1 level when Clk = 0. This causes the output to remain in its present state. Input D may be equal to 0 or 1. If D = 0 when Clk becomes 1, R changes to 0. This causes the flip-flop to go to the reset state, making Q = 0. If there is a change in the D input while Clk = 1, terminal R remains at 0 because Q is 0."

How is the value at terminal R dependent on the output Q? Is it a logical fault in the explanation? If it isn't, please explain this part of the reasoning.

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But how is the value at terminal R dependent on the output Q? Is it a logical fault in the explanation? If it isn't, please explain this part of the reasoning.

The description is certainly misleading, and its correctness is debatable. Because \$R\$ and \$Q\$ go into a NAND gate, if \$Q = 0\$ the the output of the NAND is as if \$Q = 0\$; that holds \$Q'\$ high, so as long as the preceding circuitry is holding \$S\$ high, \$Q\$ stays at zero.

It is -- I hope! -- not how I'd have described it.

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    \$\begingroup\$ I asked why the value at terminal R is dependent on the output Q. Because R is the input of the third latch and Q is its output and, as you mentioned, an input to a system should be independent of the system's output. \$\endgroup\$
    – potato
    Commented May 6, 2023 at 17:43
  • \$\begingroup\$ Whoops -- forgive me! \$\endgroup\$
    – TimWescott
    Commented May 6, 2023 at 21:44
  • \$\begingroup\$ Answer replaced -- my apologies for the earlier misfire. \$\endgroup\$
    – TimWescott
    Commented May 6, 2023 at 21:51
  • \$\begingroup\$ When CLK is low, both S and R will be high, so if Q=0, Q' must be 1. \$\endgroup\$
    – PStechPaul
    Commented May 6, 2023 at 23:10

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