Digital Electronic : Analog And Digital by Allan D. Tyler

Author:Allan D. Tyler [Tyler, Allan D.]
Language: eng
Format: mobi, azw3, pdf
Published: 2021-08-13T00:00:00+00:00

7490 4-Bit Ripple Counter with MOD-2 and MOD-5 Counter Sections

The 7490, like the 7493, is another 4-bit ripple counter. However, its flip-flops are internally connected to provide MOD-2 (count-to-2) and MOD-5 (count-to-5) counter sections. Again, each section uses a separate clock: Cp0 for MOD-2 and Cp1 for MOD5. By connecting Q0 to Cp1 and using Cp0 as the single clock input, a MOD-10 counter (decade or BCD counter) can be created. When master reset inputs MR1 and MR2 are set high, the counter’s outputs are reset to 0—provided that master set inputs MS1 and MS2 are not both high (the MS inputs override the MR inputs).

When MS1 and MS2 are high, the outputs are set to Q0 = 1, Q1 = 0, Q2 = 0, and Q3 = 1. In the MOD-10 configuration, this means that the counter is set to 9 (binary 1001).

This master set feature comes in handy if you wish to start a count at 0000 after the first clock transition occurs (with master reset, the count starts out at 0001).

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