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74490 Dual Decade Counter

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The 74LS490 (74490) IC contains two independent Decade Counting circuits. Unlike the 7490, which is a single non binary coded decimal counter, the 74490 contains two sets of outputs, each consisting of 4 lines. The sets of 4 convey the BCD representation of the decimal number 0-9. Upon completing a full cycle, the device will turn over back to zero and the user can optionally carry the overflow signal to successive stages to form a multi-digit counting machine.

This device (74490) also contains independent reset control pins, one for each counter block, allowing the designer to manipulate the counting sequence as desired. For example, using detecting logic as well as the master reset controls, the builder can create multidigit counters which reset back to zero after a count other than 9, 99, 999... etc. In a digital clock, where hours, minutes, and seconds require a double digit display respectively, the 74490 is a perfect solution to cause the necessary resets at 12/24 or 60.

Other applications may include, frequency counters, frequency dividers, and decimal registers.
Internal Logical Circuit of the 74LS490 IC (74490)

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Pinout of typical 74490 (74LS490) IC Features:

• Individual Asynchronous Clear and Preset to 9 for Each Counter
• Count Frequency — Typically 65 MHz
• Input Clamp Diodes Limit High-Speed Termination Effects