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I am currently looking at a 4017B Decade Counter Data Sheet.

As I look at the Logic Schematic for this IC (http://www.ti.com/lit/ds/symlink/cd4017b.pdf) I can see several sqaure boxes label D, C, Q(bar), Q.

Am I correct in assuming that these square boxes are a variant of the 'Flip Flop' in order to store the value that the counter is on and would I be right in assuming if I replicated this schematic with my own flip flop I could create my own Decade Counter?

Thanks.

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Correct, those are normal D flip-flops. The 4017B itself is just some D flip-flops behind a decoder, so just flip-flops wouldn't be enough to replicate the whole counter; you can use a 74xx42 or 74xx45 as the decoder after the flip-flops.

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  • \$\begingroup\$ Thankyou. Could you explain however what the decode does? I presume this just takes the logical input and produces an ON or OFF state? \$\endgroup\$ Jul 14 '13 at 9:47
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    \$\begingroup\$ It takes the binary output of the flip-flops and enables one of ten pins depending on what the value is. \$\endgroup\$ Jul 14 '13 at 9:48
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    \$\begingroup\$ Yes the 4017 uses D flips, No The 4017 is a Johnson ring 5 stage counter not a binary counter see electronics-tutorials.ws/sequential/seq_6.html This simplifies the decoding to a simple 2 input and gate for each stage. \$\endgroup\$ Jul 14 '13 at 12:38
  • \$\begingroup\$ @JImDearden: I have a feeling that the asker is more interested in replicating the effect than in duplicating the exact functionality. \$\endgroup\$ Jul 14 '13 at 23:21
  • \$\begingroup\$ @IgnacioVazquez-Abrams And to replicate the effect you need to know how the 4017 functions. This becomes important when you want to decode. By using a Johnson counter you simplify the decoding but the cost is more D type flip flops. \$\endgroup\$ Jul 15 '13 at 8:26
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The Johnson counter (4017) is a form of ring counter that takes the NOT Q output of the last stage and loops it back to the D input of the first stage. It shifts the data rather than counts it. A binary counter would only require 4 stages up to a 16 count. A 4 stage Johnson counter would only count up to 8.

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One advantage the Johnson counter has over the binary counter is how it decodes each output. The 4 stage binary counter requires inputs for all four outputs. The Johnson counter only needs 2 inputs to a simple AND gate to produce a unique output.

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