How to cycle through bits of information for a hex display?

Question

I am doing some work with a Hex Seven Segment Digital Display with a built in decoder that takes in 4 bits of information. Controlling it I have 4 cascading T-FlipFlops whose outputs are inverted so I iterate through its states backwards rather than forwards. It has the following states 1,2,3,4,5,6,7,8,9,A,b,C,d,E,F.

For example to view a 3, the first two bits are set to High, and the last two are set to off. To view an E for example the first bit is off, and the last three bits are set to High.

My problem is that I don't know how, or what is the best way, to skip the alphabetical characters, and cycle through just the numerals 1,2,3,4,5,6,7,8,9 then back to 0. What is the best way to do this.

I'm not coding, there are no micro-controllers this is all digital logic.

Answer 1

Use a decade counter like the 74xx90. If you need two then choose the 74xx390

Answer 2

It's not easy to do with T flip-flops if they don't have reset inputs. Basically, what you want to do is when the counter hits 9, the next cycle will reset it back to zero. Or alternatively, when it his 10 you immediately assert the flip-flop resets to set it back to zero. So you will need a 4 bit comparator to compare the counter outputs with either 9 or 10, and then a way to reset the counter to zero. There are also counter chips called 'decade counters' available which contain this logic internally so they will count up to 9 and then recycle back to 0.