Question

Complete this AVR assembly language fragment so that it adds the unsigned 16-bit value in register pair r9:r6 to the unsigned 16-bit value in r7:r8. (Registers 9 and 7 are the most signficant bytes in these 16-bit quantities. The result ends up in r7:r8.)

addadcadiwr6r7r8r9  addadcadiwr6r7r8r9 ,  addadcadiwr6r7r8r9
addadcadiwr6r7r8r9  addadcadiwr6r7r8r9 ,  addadcadiwr6r7r8r9

Answer 1

/* Add the unsigned 16-bit value in register pair r9:r6 to the unsigned 16-bit value in r7:r8. The result ends up in r7:r8. */

.include "m328-pdef.inc" ; Includes AVR related functions

.eq    rstart = 0x00
.def    r1 = r9:r6 ;defining registers
.def    r2 = r7:r8 ;defining registers
.ds ; data segment
.org rstart
r3: .byte 2 ;holds 16 bit registers r9:r6
r4: .byte 2 ;holds 16 bit registers r7:r8
.cseg
.org 0x00
jmp begin ; jump to loop begin

begin:
    movw r3,r1 ; move the content of r1 to r3
    movw r4,r2 ; move the content of r2 to r4
    add r3,r4  ; add the content and store in r3
    ret        ; return the computed result