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I have this question but I don't know what happen to a dff without an input is it always 0 ?? like this picture below the 2nd dff hasn't any d ??? Also, if someone can draw the answer of the question ? thank you enter image description here

and I would like t

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    \$\begingroup\$ Floating inputs are indeterminate. \$\endgroup\$ – Chu Dec 14 '18 at 1:18
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After the asynchronous reset is deasserted and the first rising clock edge occurs, the flip-flop's state will generally be indeterminate. The only way the state could have a known value is if the flip-flop's inputs have a known value when they are unconnected, due to the specific circuitry involved. For example, true TTL logic inputs would default to a high logic level if left unconnected.

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  • \$\begingroup\$ By the same token, a CMOS flip-flop can do the most amazing things if the input is left floating. It can oscillate, or it can even be affected by the behavior of the other FF (assuming that we're talking about a dual FF on a chip). \$\endgroup\$ – WhatRoughBeast Dec 14 '18 at 6:00
  • \$\begingroup\$ So here the value of A1 is zero all the time because we put on the reset ? \$\endgroup\$ – user207243 Dec 14 '18 at 13:19
  • \$\begingroup\$ No, the reset signal is deasserted before the first clock edge. So you know that both flip-flops are set to 0 before the first clock. \$\endgroup\$ – Elliot Alderson Dec 14 '18 at 14:10

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