Chapter 14

Designing with Logic ICs

Tim Williams

14.1 Logic ICs

The interfaces between logic integrated circuits including signal, clock and power supply lines must be considered to achieve a reliable digital design. This applies whether the devices concerned are microprocessors, their support chips, application specific ICs (ASICs), programmable logic arrays (PLAs) or standard “glue” logic.

14.1.1 Noise Immunity and Thresholds

A logic input can take any value of voltage, nominally from one supply rail to the other, although due to transmission line effects the actual voltage can exceed either supply rail on transitions. Each input is designed so that any voltage below one level, conventionally VIL, is regarded as a logic “0” and any voltage above ...

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