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\lhead{\bfseries EE 308 }
\chead{\bfseries }
\rhead{\bfseries Spring 1998}
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\begin{center}
{\bf Using the HC12 Pulse Accumulator}
\end{center}


The Pulse Accumulator measures events on Bit 7 of Port T
\begin{enumerate}
\item Event count mode.  Examples of use:  Count number of people entering
room.  Count number of revolutions of a wheel in one second to determine speed
(in RPS).
\begin{enumerate}
\item Enable PACTL (Set bit {\tt PAEN} in the {\tt PACTL} register)
\item Set mode to event count (Clear bit {\tt PAMOD} in the {\tt PACTL}
register)
\item Choose edge with {\tt PEDGE} bit of {\tt PACTL} register: \\
{\tt PEDGE = 0 =>} count falling edges\\
{\tt PEDGE = 1 =>} count rising edges
\item Clear 16-bit PACNT register (if desired)
\item If desired, enable interrupt on any selected edge -- set {\tt PAI} bit
of {\tt PACTL} register
\item If desired, enable interrupt on {\tt PACNT} overflow -- set {\tt PAOVI}
bit of {\tt PACTL} register
\item When desired, read {\tt PACNT} register to determine how many events
have occurred.
\end{enumerate}
\item Gated time accumulation mode -- Example of use: Determine the length of a pulse
\begin{enumerate}
\item Enable timer (Set bit {\tt TEN} in the {\tt TSCR} register)
\item Enable PACTL (Set bit {\tt PAEN} in the {\tt PACTL} register)
\item Choose whether to count when input is high or input is low \\
{\tt PEDGE = 0 =>} count when input high\\
{\tt PEDGE = 1 =>} count when input low
\item Clear 16-bit PACNT register (if desired)
\item If desired, enable interrupt on selected edge -- set {\tt PAI} bit
of {\tt PACTL} register
\item If desired, enable interrupt on {\tt PACNT} overflow -- set {\tt PAOVI}
bit of {\tt PACTL} register
\item When desired, read {\tt PACNT} register to determine how clock edges 
have occurred while input is in active state.
\end{enumerate}
\end{enumerate}

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