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\begin{document}
\title{Parallel Input/Output}
\date{}
\author{N. Narasimhamurthi}
\maketitle
\section{Objective}
To become familiar with hardware interfacing and input/output.
Also introduces polling timer overflow flag.
\section{Getting started}
It is extremely important that you become familiar with your HC11.
Since most of you will be using the {\tt CMD11E1} board made by
Axiom Manufacturing, this write-up is specific to the board.

\begin{enumerate}
\item
Locate the jumper {\tt JP13} and make sure that it is open.
\item Locate the MCU port. This is a dual row 17-pin Berg style
connector. Locate pin \#1 on the port. This is identified with the
number 1 on the front of the board. On the other side (solder
side), pin \#1 is identified by a square solder.
\item
Connect a ribbon cable to the port. Use a continuity tester to
locate and identify the following pins: pin 1 (PA0), pin 5 (PA4),
pin 6 (PA5), pins 9 and 10 (5 Volts),  pins 11 and 12 (Ground).
(See page 15 of the User's guide that came with your board.)
\item
Make two test light emitting diode probes. It is a good idea to
have several probes handy. To make a test probe, connect a 3.3K
resistor to the {\bf anode} of a light emitting diode (See figure
\ref{fig:probe}). Use a light emitting diode with an operating
voltage of 1.7 volts and a current rating in the 1-5 mA range. If
you use an light emitting diode with 20+ mA operating current, the
light emitting diode would be dim when it lights up and you may
have to look carefully to see if it is on. Test the probe by
connecting the free end of the resistor to pin 9 and the free end
of the light emitting diode to pin 11. The light emitting diode
should light-up. If not, the chances are you have connected the
resistor to the cathode of the light emitting diode. Redo your
circuit by connecting the resistor to the anode.
\end{enumerate}
\placedrawing{fig1.lp}{\em Test Probe. Make sure that the resistor
is connected to the anode of the light emitting diode. The longer
lead of the light emitting diode is the anode. To test a pin,
connect the cathode to ground and the resistor to the pin.
}{fig:probe}
\section{Experiment}
\subsection{Hardware connection}
\begin{enumerate}
\item
{\bf Disconnect the power to HC11.}
\item
Connect a (LEFT) test probe between pin 5 and pin 11. The cathode
of the light emitting diode should be connected to pin 11 and the
free end of the resistor to pin 5.
\item
Connect a (RIGHT) test probe between pin 6 and pin 12. The cathode
of the light emitting diode should be connected to pin 12 and the
free end of the resistor to pin 6.
\item
Label the two light emitting diodes as LEFT and RIGHT so that it
is easy to identify them (you can use a magic tape and small
pieces of paper).
\item
Connect the input circuit as shown in figure \ref{fig:2}.
\item
Check and recheck all your connections before you connect the
power to the HC11.
\end{enumerate}
\placedrawing{fig2.lp}{\em Typical input connection }{fig:2}
\subsection{Theory of operation}
Port A in HC11 appears at memory location {\tt \$1000}. In port A,
the bits 0,1 and 2 (referred to as PA0, PA1 and PA2) are inputs.
They appear as pins 1, 2, and 3 of the MCU port (this is specific
to the Axiom Board. If you use a different board, check the
documentation that came with your board). Thus if you read the
memory location \verb+$1000+, then the value in the bits depends
on the voltage applied to the corresponding pins. If the voltage
is 5 Volts, the bit will be one, and if the voltage is zero, the
bit would be zero.

Bits 3,4,5 and 6 of port A (referred to as PA3, PA4, PA5 and PA6)
are outputs. This means your program can control the voltage in
the corresponding pins 4,5,6 and 7 by writing a 1 or a zero to the
appropriate bit in location \verb+$1000+.
\subsection{Experiment 1}
Use memory modify, \verb+MM $1000+, command to modify the location
\verb+$1000+. Change the value in the location to \verb+$00+,
\verb+$10+, \verb+$20+, and \verb+$30+. (Note: When you
communicate directly with the HC11 using BUFFALO commands, you do
not type the \verb+$+.) After each change, look at the state of
the light emitting diodes and write down what you see. Provide a
brief explanation of what you see.

Using the methods you learnt in earlier labs, write a program that
will read the keyboard and depending on what the user types,
perform the following:
\begin{center}
\begin{tabular}{|l|l|}
  \hline
  % after \\: \hline or \cline{col1-col2} \cline{col3-col4} ...
  Key  & Action \\ \hline
 \verb+Q+ or \verb+q+ & Turn on the LEFT led. The state of other led should not change. \\
 \verb+Z+ or \verb+Z+ & Turn off the LEFT led. The state of other led should not change. \\
 \verb+E+ or \verb+e+ & Turn on the RIGHT led. The state of other led should not change. \\
 \verb+C+ or \verb+c+ & Turn off the RIGHT led. The state of other led should not change. \\
 \hline
\end{tabular}
\end{center}
\subsection{Experiment 2}
Use memory dump to see the contents of \verb+$1000+. Close the
input switch and dump the contents of location \verb+$1000+.
Repeat the experiment with the switch open. Write down what you
see and provide a brief explanation of your observation.

Write a program that will, in an infinite loop, print either
\verb/CLOSED/ or \verb/OPEN/, depending on the state of the
switch. The program should continually monitor the state of the
switch, and print \verb/CLOSED/ is the switch is closed. Or else
it should print  \verb/OPEN/.
\section{Timing}
In this part of the lab, we will monitor the {\tt TOF} flag. This
flag is controlled by the {\em free running counter}. The free
running counter is a 16 bit counter that counts the clock ticks.
It is set to {\tt \$0000} on power up. It counts up to {\tt
\$FFFF}and then rolls over to {\tt \$0000} and the process is
repeated until you power off the HC11. Every time the counter
rolls over, it sets the {\tt TOF} flag. This flag is not
automatically reset and it is your responsibility to reset it in
your code depending on your need. To reset the flag you have to
write a 1 to it \footnote{This is true of all HC11 flags. You
reset a flag, i.e. make it go to zero, by writing a 1 to it!}.

Your HC11 most likely uses a 8 MHz crystal which means that the
processor speed is 2 MHz, or you get $2 \times 10^6$ clock ticks
every second. The free running counter rolls over every $2 ^{16}$
ticks, or you get
\[
\frac{2 \times 10^6}{2^{16}} = 30.52 ~~\mbox{overflows every
second}
\]
We can use this to create a $\frac{30.52}{2}$ Hz square wave by
toggling an output pin every time counter rolls over. Here is the
code (you have to fill in the details!)
\begin{verbatim}
; Various defines go here ...
       ORG $3000 don't forget the $
ME     FCC /Your name/
       FCB 10
       FCC /ECE 372/
       FCB 10
       FCC /Date the program was last changed/
       FCB 10, 10, 4

       ORG $2000 DONT FORGET THE $
       LDX #ME
       JSR OUTSTRG ; MAKE SURE YOU HAVE EQU FOR OUTSTRG

LOOP1
; CLEAR THE FLAG. NO HARM IS DONE IF IT IS ALREADY CLEARED
       LDAA #%10000000
       STAA TFLAG12

;WAIT FOR THE FLAG TO BE SET
LOOP2
      LDAA TFLAG2
      ANDA #%10000000
      BEQ LOOP2

;NOW TOGGLE PA4
      LDAA #%00010000
      EORA PORTA
      STAA PORTA

;DO IT ALL OVER AGAIN
      BRA LOOP1
\end{verbatim}

Type and run the above program. Connect the LED to PA4 (pin \#5)
and you should see it flicker. Connect the pin to a oscilloscope
and verify that you are generating a square wave. Verify that the
frequency is correct.
\end{document}