7490: Decade Counter (÷10) (Ripple, Not Presettable, Not Unit-Cascadable)

This is a divide-by-2 and a divide-by-5 counter in a single package. They may be used together as a divide-by-10 or separately. It ripple-counts in the BCD-up direction. Note the unusual supply pinouts.

For a BCD counter, weighted 1-2-4-8, enter via Clock 1, and iumper Q1 to Clock 2. Both 9-Set and both 0-Set inputs must be grounded for normal counting.

The counter advances on the negative-going clock edge. The clock must be properly conditioned and made bounceless and noise free. If a conventional decade counter is needed, all set terminals must be held at ground.

The counter may be reset to zero by bringing either or both 0-Set inputs positive. The counter may be preset to 9 by bringing either or both 9-Set inputs positive.

An external jumper must be provided between counter halves. If entry is via Clock 2, and Q8 is jumpered to Clock 1, a counter weighted 1-2-4-5 results, with Q1 as the most significant output and a symmetrical square wave at the output. The circuit is not unit-cascadable.

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