The digital 'or' gate is an n-input, single-output 'or' gate which produces
an active "1" value if at least one of its inputs is a "1" value. The gate
produces a "0" value if all inputs are "0"; if neither of these conditions
holds, the output will be unknown. The delays associated with an output rise
and those associated with an output fall may be specified independently. The
model also posts an input load value (in farads) based on the parameter
input_load. The output of this model does NOT, however, respond to the total
loading it sees on its output; it will always drive the output strongly with
the specified delays.