Count Number of Students who Pass
Homework Assignment
Write an MC68000 program that will examine a list of test scores stored in memory.
Transfer any passing score (greater than or equal to 50) to a table in memory, and transfer
any failing score to another table in memory. Also, keep a count of the number of scores
in each table.
• Assume that twenty scores are stored in memory words starting at location $5000.
Define this table of words, and assign a label to it using the DS.W assembler
directive. (How do you force its location to $5000?)
• Store all passing scores in memory words starting at location $5100, and store all
failing scores starting at location $5200. Define these tables using DS.W
assembler directives.
• Store the final count for the number of passing scores in register D2 and the
number of failing scores in register D3.
• Start your program at location $800.
• Include all necessary global and local comments.
• Use numbers to represent addresses only in ORG directives; for other instructions,
use labels.
• Clear your tables of passing and failing scores using program instructions at the
start of your program, to prepare for repeat runs.
• Do not leave any blank words between scores in either table.
• Try your program several times, with different data
• The name of your program should be your last name or its first eight letters.
Submit your program file (with extension .X68) and representative results as a
hard copy in the class prior to the due date.
Solution for Assignment 5:
ORG $800
START
LEA PASSING,A1 ; load address of passing scores into A1
LEA FAILING,A2 ; load address of failing scores into A2
MOVE #20,D1 ; we will use D1 as a counter for the 20 positions
FILL
MOVE.W #0,(A1) ; clear the current position in the passing table
MOVE.W #0,(A2) ; clear the current position in the failing table
ADD #2,A1 ; go to next position in the passing table
ADD #2,A2 ; go to next position in the failing table
SUB #1,D1 ; decrement position counter
BNE FILL ; if it’s not zero, repeat
LEA SCORES,A0 ; load address of scores into A0
LEA PASSING,A1 ; load address of passing scores into A1
LEA FAILING,A2 ; load address of failing scores into A2
MOVE #0,D2 ; initialize number of passing scores to zero
MOVE #0,D3 ; initialize number of failing scores to zero
MOVE #20,D1 ; we will use D1 as a counter for the 20 scores
COUNT
MOVE.W (A0),D0 ; load a score from the array
CMP.W #50,D0 ; compare with 50 to see if it’s a passing or failing score
BLT FAIL ; if it’s lower than 50 it’s failing
MOVE.W D0,(A1) ; otherwise it’s a passing score, save it in the passing table
ADD #2,A1 ; increment the pointer to the next empty space in the passing table
ADD #1,D2 ; increment the number of passing scores
BRA NEXT ; go to next element by skipping the fail part
FAIL
MOVE.W D0,(A2) ; it’s a failing score, save it in the failing table
ADD #2,A2 ; increment the pointer to the next empty space in the failing table
ADD #1,D3 ; increment the number of failing scores
NEXT
ADD #2,A0 ; go to next score in the table
SUB #1,D1 ; decrement score counter
BNE COUNT ; if it’s not zero, repeat
MOVE.L #9,D0 ; end program
TRAP #15
ORG $5000
SCORES DS.W 20
ORG $5100
PASSING DS.W 20
ORG $5200
FAILING DS.W 20
END START
*~Font name~Courier New~
*~Font size~10~
*~Tab type~1~
*~Tab size~4~