AMD Am186 Series, Instruction Set

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Instruction Set 4-247
XCHG XCHG
This example performs a bubble sort on a list of unsigned numbers in memory. The
microcontroller rearranges the list from smallest to largest.
Tips
To exchange two components that are both stored in memory, use MOV to copy the first
component to a register, use XCHG to exchange the register with the second component,
and then use MOV again to copy the register to the first component.
X
CHG requires both operands to be the same size. To convert an 8-bit integer to its 16-
bit equivalent, use CBW. To convert a 16-bit integer to its 32-bit equivalent, use CWD. To
convert another type of component to its extended equivalent, use MOV to copy 0 to the
high byte or word.
You cannot use XCHG to exchange a word with a segment register. To copy a segment
address to a segment register, use MOV to copy the segment address to a general register,
and then use MOV to copy the value in the general register to the segment register.
Related Instructions
If you want to See
Copy a component to a register or a location in memory MOV
LIST DB 3,5,2,9,7
L_LENGTH EQU 5
; sort unsigned numbers
MOV SI,0 ; set up list index
MOV DX,L_LENGTH - 1 ; get length of list
MOV CX,DX ; set up counter
SORT:
MOV AL,LIST[SI] ; copy this number
CMP AL,LIST[SI]+1 ; is this number <= next number?
JLE NEXT ; if so, then jump
XCHG AL,LIST[SI]+1 ; write larger number to next byte
MOV LIST[SI],AL ; write smaller number to this byte
NEXT:
INC SI ; point to next number
LOOP SORT ; while CX is not zero, jump
; to top of loop
DEC DX ; set up length of sublist
MOV SI,0 ; reset sublist index
MOV CX,DX ; set up sublist counter
LOOP SORT ; while CX is not zero, jump
; to top of loop