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Bebop to the Boolean Boogie, 3rd Edition by Clive Maxfield

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Appendix A. Assertion-Level Logic

Beware—Here Be Dragons!

In ancient times, the phrase “Beware, here be dragons!” was penned on maps to indicate unknown territory. Today, the same words of caution should be applied to the terms active-high and active-low, which are subject to confusion. Some academics (and even textbooks) define an active-low signal as one whose asserted (active) state is at a lower (more negative) voltage level than its unasserted (inactive) state. On this basis, an active-high signal would be one whose asserted state is at a higher (more positive) voltage level than its unasserted state. Although these definitions may work most of the time, they cause confusion when combined with negative logic implementations.[1]

1 Negative ...

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