Hardware and Software Development Tools for the HCS12 - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 119

ldx array ; place the starting address of array in X

movw 0,sum ; initialize sum to 0

ldy N ; initialize loop count to N

loop ldab 1,x 1 ; place one number in B and move array pointer

sex B,D ; sign-extend the 8-bit number to 16-bit

addd sum ; add to sum

std sum ; update the sum

dbne y,loop ; add all numbers to sum yet?

swi ; return to monitor

end

At first look, this program appears to be fine and should work. After assembling the pro-
gram, we download it onto the demo board and get the following screen output:
. load
....
done
.
It is a good idea to make sure that the program has been downloaded onto the demo board
by using the asm command.
+ asm 1500
xx:1500 FE1000 LDX $1000 .
xx:1503 180400001014 MOVW $0000,$1014 .
xx:1509 DD14 LDY $0014 .
xx:150B E630 LDAB 1,X 1 .
xx:150D B714 SEX B,D .
xx:150F F31014 ADDD $1014 .
xx:1512 7C1014 STD $1014 .
xx:1515 0436F3 DBNE Y,$150B .
xx:1518 3F SWI .
Indeed, the program is downloaded correctly. The next thing to check is to make sure that
the array data is downloaded correctly by using the md command.
+ md 1000 1010
1000 02 04 06 08 - 0A 0C 0E 10 - 12 14 16 18 - 1A 1C 1E 20 . . . . . . . . . . . . . . .
1010 22 24 26 28 - 00 00 B9 A9 - 2A CA FA DB - AC DA 18 97 “$&(. . . .*. . . . . . .
.
Again, we are convinced that the data array has been downloaded correctly. The array is
stored at locations from $1000 to $1013. The variable sum occupies the memory locations from
$1014 to $1015. Since the program has not been run yet, these 2 bytes contain 0s.
The next thing to do is to run the program. This program should run to the swi instruction
and stop. The screen should look as follows:
+ g 1500
User Bkpt Encountered
PP PC SP X Y D 5 A:B CCR 5 SXHI NZVC

38 1519 3C00 0213 0000 FF:07 1001 1000

xx: 1519 88F4 EORA #$F4

.