16-bit addition
Purpose:
To add the contents of the 16-bit variable value1 and location $6000 to the contents of the 16-bit variable value2 at location 6002 and place the result in the 16 bit variable result at location $6004.
Sample Test Data:
input:
value1: (6000) = 10F5
value2: (6002) = 2621
output:
result: (6004) = 3716
Recall that ( ) means "contents of". Also when we
write (6000) = 10F5 we in fact mean (6000) = 10 and (6001) = F5.
Source Code:
Version 1
| data | equ | $6000 | |
| program | equ | $4000 | |
| org | data | ||
| value1 | ds.w | 1 | ;first value |
| value2 | ds.w | 1 | ;second value |
| result | ds.w | 1 | ;to contain result |
| org | program | ||
| move.w | value1, d0 | ;get first value | |
| add.w | value2, d0 | ;add numbers together | |
| move.w | d0, result | ;store result |
Source Code:
Version 2
This way of doing it is wasteful
of time and effort on the both the programmer's and the
computer's part.
It is provided as a way of introducing indexed addressing in an
easy way. Normally such addressing
is used in the context of a loop where, on each pass through the
loop, access is made to the next element in
a list.
equ and ds operations as for version 1
| org | program | ||
| movea.l | #value1, a0 | ;make a0 point to value1 | |
| move.w | (a0), d0 | ;first value to d0 | |
| adda.l | #2, a0 | ;make a0 point to value2 | |
| add.w | (a0), d0 | ;add numbers together | |
| adda.l | #2, a0 | ;make a0 point to result | |
| move.w | d0, (a0) | ;store contents of d0 in wherever a0 is pointing to, i.e. into the variable result |