DIGI book chapter 11 Synchronous counters 11.3 underneath the graphic titled "A four-bit synchronous " down" counter". In the first sentence it says, "...we can build a counter circuit with selectable between "up" and "down" count modes...". It should be, "...we can build a counter circuit with selectability between "up" and "down" count modes..." or "...we can build a counter circuit with selectable "up" and "down" count modes...".

 

Or we could go with more correct grammar.

In any case, verified.

http://www.allaboutcircuits.com/vol_4/chpt_11/3.html

Is:

Taking this idea one step further, we can build a counter circuit with selectable between "up" and "down" count modes by having dual lines of AND gates detecting the appropriate bit conditions for an "up" and a "down" counting sequence, respectively, then use OR gates to combine the AND gate outputs to the J and K inputs of each succeeding flip-flop:

Should be:

Taking this idea one step further, we can build a counter circuit that is selectable between "up" and "down" count modes by having dual lines of AND gates detecting the appropriate bit conditions for an "up" and a "down" counting sequence, respectively, then use OR gates to combine the AND gate outputs to the J and K inputs of each succeeding flip-flop:

 

That will also work. I'm on a tablet and typing with my thumbs. I think I would have to use at least one example of how it could be changed to best point out the error. Would you like me to provide more possibilities for revision in my feedback?

 

Not really, one is enough, and good enough is enemy of the best.

This is a situation for KISS, Keep It Simple Stupid. When our editor comes through he will appreciate both the help and brevity.