EECE 259 - Lab 5 - Using The Assembler and Debug Monitor.pdf

Part E – Modifying a Program
Go back to the IDE68k/Assembler and open up the original program you typed in
at the start of the Lab, the one that copies Switches to LEDS.
Modify the program to do the following. For each change, download, disassemble
and single step the new version of the program.
o Read Port B (switches 8-15) and copy the data to the red leds 8-15 and
also the Hex0 Display (look up the addresses of these output ports in the
lecture notes and handouts on using the 68000 on the DE2 board).
o Store the data you read from Port A and Port B to Static Memory at
addresses $00010000 and $00010001. Single step this program and set up
watch points on these two address to observe them change.
Part F – Writing your own program
Write an assembly language program to read in your 8 digit student number using the
slider switches SW0-SW7 on the DE2 board (note these switches are connected to
one of the input ports) and display them on the 8 digit hex displays. To make it
simple, assume your student number only contains digits in the range 0-7 (not 8 or 9)
as this means we do not have to read the other input port where switches 8 and 9 are
connected.
For example, if your student number was 56231447, then you would enter this by
moving SW5 to the up position then back to the down position, followed similarly by
Switches 6,2,3,1,4,4,7. Your software will have to read the switch port, detect when a
switch has moved to the up and then down position and write data to the Hex
displays.
You should investigate the BNE (branch if not equal to zero instruction) and BEQ
(branch if equal to zero instruction) to determine when the switch has been pushed up
or returned to the down position (logic 0). This can be explained as follows.
When the switch is in the up position (logic 1), and you read the value of the switches
into 68000 register d0, it will clear the ‘Z’ bit in the 68000 condition code register.
When the switches are in the down position (logic 0), reading the switches will set the
‘Z’ bit. BNE and BEQ branch if the Z bit is 0 or 1 respectively.
Note you can expect some occasional “contact bounce” on the switches leading to
occasional incorrect detections of up/down movement (this is normal for a
mechanical switch)
When all 8 digits of your student number have been read, the program should stop
and return to the debug monitor with a TRAP #15 instruction. Use the debugger to
single step and debug the program.
Write an assembly language program to read the 1st first 4 digits of your student
number and convert them into a 16 bit (4 digit) BCD number. For example, if the first