Abstract
A NULL convention logic element comprises an input, and output and a
threshold switching circuit. The input receives NULL convention
signals that are encoded onto a plurality of physical input signal
lines that can assume at least a first meaningful signal state
indicating data, a NULL signal state which has no logic meaning and
third signal state distinct from the first and second signal states.
The output produces output NULL convention signals that are encoded
onto a plurality of physical input signal lines that can assume at
least a first meaningful signal state indicating data, a NULL signal
state which has no logic meaning and third signal state distinct from
the first and second signal states. The threshold switching circuit
triggers changes of the output signal state to NULL in response to the
states of all the input signals becoming NULL. The threshold
switching circuit triggers changes of the output signal state to the
meaningful state when the number of input signals in the meaningful
state exceeds a threshold number. The threshold switching circuit
triggers changes of the output signal state to the third state when
(i) fewer than all input signals are in the NULL state, and (ii) fewer
than the threshold number of input signals are in the meaningful
state.