74390 - decade counter with T FFs

Jam Clear when High

Have a toggle only (FF A) and a counter to 4 (FFs B to D) with separate clocks input A and B respectively.

to make decade counter connect QA to INB

To see how this works we notice that the AND gate on the input clock for FF B is disabled when QD is High so no counting occurs past 8. Furthermore at QA= QD=1 and QB= QC=0 the next falling edge of INA makes both QA and QD go low, starting the count over.