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.
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.
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.
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.
