University of Florid a EEL 4744
Department of Electrical and Computer Engineering
Page 1/2
Lab #4: Elementary Programming & Adding a Keypad
Purpose
The purpose of th is lab is to give students more
practice in writing and debugging elementary
assembly routines. In addition to this, students
will learn how to add a simple keypad to their
6812 boards and how to scan it properly to
eliminate switch bounce.
Part I. Writing Assembly - Sort Routine
You will be given a vector containing 2’s
complement 8 bit numbers. You task is to write a
routine that copies these numbers over to a new
vector (in RAM) in order of magnitud e. The
largest number should be written first in the new
vector and the smallest number should be last.
1. You are not allowed to corrupt the original
vector that you are sorting. You are also not
allowed to use the 68HC12 Max & Min
functions. Write your own using conditional
branches.
2. You should test your routine with a test vector
of data (created by you).
3. In lab your TA will give you the address of the
vector to be sorted (orig_addr), the length of this
vector (orig_len) and the new sorted v ector’s
address (sorted_addr).
4. All code should be easily relocate-able in
memory. You should write your sort routine as a
subroutine and call it from your main program.
5. Pass parameters to your subroutine via the
stack. Parameters should be placed on the stack
(in the main program) in the following order:
1. orig_addr
2. orig_len
3. sorted_addr
6. Your sort subroutine does not pass any values
back to the main but instead creates the sorted
vector in memory specified by “sorted_addr”.
7. Your code shou ld be original and not match
your classmates code (a data mining software
will be used to exa mine all submitted code and
check identical code). Copied Cod e will result
in a zero for the lab.
Part II. Adding a Keypad
1. Connect the keypad given in your lab kit such
that COL 4:1 are directly connected to Port P3:0.
Note: It is best to place the keypad on top of the
development board with the pins facing up
nearest the port headers. See the diagr am at the
end of this lab documentation for more detail.
2. Connect the keypad ROW 4:1 signals to pull-
up resistors and Port P7:4.
3. Using the Monitor, set DDRP such that Port
P7:4 are inputs and Port P3:0 are outputs. We
will use the lower nibble on Port P to send out a
known pattern and then we will check for this
pattern on the upper nibble (input) of Port P.
4. Try writing out a "E" (hex) on Port P and read
the value in with no key pressed (should be "F").
5. Now press the "1" key and read the port. An
"E" should be read back. Next, press "4" on the
keypad and read the port. A "D" should be read
back. The "E" output pattern places a "L" only
on COL1 and so when we read this low in on a
particular row, the pattern read in indicates
whether it is "*", "7", "4" or "1" on the keypad.
********** Very Important Note **********
On ly pr ess one ke ypa d but ton at a
ti me. If y ou pr es s two keyp ad b utto ns,
it is p oss i bl e t o sh ort t wo out pu ts
to get he r wh ic h ma y da mage Por t P
an d po ssi bl y de st r oy t he 681 2 IC .
***************************************
6. Write a program that cycles a pattern of $7,
$B, $D and $E over and over. Essentially, we
are sending out only one "L" on a pin and
cycling it through COL 4:1. Next, read in the
port value that corresponds to keypad ROW 4:1
and using both pieces of information determine
which key has been pressed on the keypad. Send
this value to your binary display.
