The NOR gate is a digital logic gate that implements logical NOR. A HIGH output (1) results if both the inputs to the gate are LOW (0); if one or both input is HIGH (1), a LOW output (0) results. NOR is the result of the negation of the OR operator. NOR is a functionally complete operation—combinations of NOR gates can be combined to generate any other logical function. By contrast, the OR operator is monotonic as it can only change LOW to HIGH but not vice versa.
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module nor1(c,a,b); output c; input a,b; wire d; or1 u1(d,a,b); inv u2(c,d); endmodule