\section{Analog Input as Digital Input}
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\textit{Platforms: all}
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The \textit{ainput\_as\_dinput} driver is a digital input driver that 
makes use of an available analog input as if it were a digital input.
The MX record database entry for this driver specifies how to interpret
the analog input voltages to decide whether or not to report the current
``digital input'' state as Low or High.  Three voltage levels are specified
there:

\ \newline
\MxAinputZasZdinputDriverFields
\newline

The \textit{low\_voltage} field is used to specify the nominal analog input
voltage that corresponds to the digital Low (0) state.  Similarly, the 
\textit{high\_voltage} field is used to specify the nominal analog voltage
for the digital High (1) state.  \textit{threshold\_voltage} is used to specify
the boundary between the two states.

Please note that the analog voltage corresponding to the Low state can
actually be higher than the analog voltage corresponding to the High state
if we are implementing negative logic.  All that is required is that
the value of \textit{threshold\_voltage} be between the ``low''
and ``high'' voltages.
