Quiz 2
ECE-3120: Fall ‘08
1) Write an instruction sequence to add two 16 bit numbers stored at $2000-$2001 and
$2002~$2003 and subtract the 16 bit number stored at $1000 from the sum. Store
the result in $$2100
org $1000 ;starting address of the program
ldd $2000 ;DÅm[$2000]
addd $2002 ;DÅm[$2002]
subd $1000 ;DÅm[$1000]
std $2100 ;DÅm[$2100]
2) Write a sequence of instructions to compute the sum of N signed 8-bit numbers stored
at memory locations $1000 and store the result in $2000
N equ 5 ;array count
org $1000 ;starting address of the array
array: db 1,2,3,4,5
org $2000 ;starting address of the array
sum: rmb 1 ;array sum assuming we need just 1 byte
i: rmb 1 ;array index
org $1500 ;starting address of the program
ldaa #0
staa i ;initialize loop (array) index to 0
staa sum ;initialize sum to 0
loop: ldab i
cmpb #N ;is I = N?
beq done ;if done, then branch
ldx #array ;use index register X as a pointer to the array
abx ;compute the address of array[i]
ldab 0,x ;place array[i] in B
ldy sum ;place sum in Y
aby ;sumÅsum+array[i]
sty sum ;update sum
inc i ;increment loop counter by 1
bra loop
done: swi ;return to D-Bug12 monitor
end
