HCS12 Assembly Programming - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 68

Example 2.14
▼ Write a program to add an array of N 8-bit numbers and store the sum at memory locations
$1000,$1001. Use the “for i 5 n1 to n2 do” looping construct.
Solution: We will use variable i as the array index. This variable can also be used to keep track
of the current iteration being performed. We will use a 2-byte variable sum to hold the sum of
array elements. The logic flow of the program is illustrated in Figure 2.9. The program is a di-
rect translation of the fl owchart in Figure 2.9.

Start

i ← 0
sum

← 0

Yes

i = N? Stop

No

sum ← sum + array[i]

i ← i + 1

Figure 2.9 ■ Logic flow of example 2.14

N equ 20 ; array count

org $1000 ; starting address of on-chip SRAM

sum rmb 2 ; array sum

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

staa sum 1 1 ; “

loop ldab i

cmpb #N ; is i 5 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 ; compute sum <- sum 1 array[i]

sty sum ; update sum

inc i ; increment the loop count by 1

bra loop