AMD Am186 Series, Instruction Set

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Instruction Set 4-164
NEG NEG
Examples
This example uses addition to find the difference between two integers.
This example copies a string of 8-bit integers stored in memory to another string located
in the same segment. The microcontroller copies the bytes and changes their sign—one
by one, from first to last—before storing them in the other string.
Related Instructions
If you want to See
Toggle all bits of a component NOT
Subtract a number and the value of CF from another number SBB
Subtract a number from another number SUB
INTEGER1 DW 2000 ; 7D0h
INTEGER2 DW 1600 ; 640h
; calculate difference using sign change and addition
NEG INTEGER2 ; INTEGER2 = F9C0h = -1600
; signed addition: INTEGER1 = IN INTEGER2
ADD INTEGER1,INTEGER2 ; INTEGER1 = 0190h = 400
; defined in SEG_C segment
SOURCE DB 20 DUP (?)
DESTINATION DB LENGTH SOURCE DUP (?)
; notify assembler: DS and ES point to the
; same segment of memory
ASSUME DS:SEG_C, ES:SEG_C
; set up DS and ES with same segment address
MOV AX,SEG_C ; load segment into DS and ES
MOV DS,AX ; DS points to SEG_C
MOV ES,AX ; ES points to SEG_C
; initialize and use source string
...
; save ES
PUSH ES
; set up registers and flags
LEA SI,SOURCE ; load source offset (segment = DS)
LEA DI,DESTINATION ; load dest. offset (segment = ES)
MOV CX,LENGTH SOURCE ; set up counter
CLD ; process string low to high
LOAD:
LODSB ; copy integer to AL
NEG AL ; change sign of integer in AL
STOSB ; copy AL to destination string
LOOP LOAD ; while CX is not zero,
; jump to top of loop
; restore ES
POP ES