ECT 2440 Study Guide - Final Guide: Sequential Logic, Nor Gate, Combinational Logic
Document Summary
So far we have investigated combinational logic for which the output of the logic devices/circuits depends only on the present state of the inputs. This implies that a sequential logic device has some kind of memory of at least part of its history (i. e. , its previous inputs). Sequential logic devices have some sort of feedback, where the output of some logic device is fed back to the input of a logic device. A simple memory circuit constructed from a or gate is shown on figure 1. In this memory device, if a and q are initially at logic 0, then q remains at logic 0. However if a becomes a logic 1, then the output q will be logic 1 ever after, regardless of any further changes in the input at a. Once q = 1 has been written it can"t be changed back but it can be read.
