add ax, dx; ---> ax = ax+dx
adc ax, dx; ---->ax = ax+dx+carry(进位)
sub ax, dx; ----> ax = ax - dx
sbb ax, dx; ------> ax = ax - dx - carry
assume cs:code, ds:data, ss:stack
data segment
db 128 dup(0)
data ends
stack segment
db 128 dup(0)
stack ends
code segment
start: mov dx, stack
mov ss, dx
mov sp, 128
mov ax, 0FFFFH
mov dx, 1000H
add ax, 0FFFFH
adc dx,0
mov ax, 4C00H
int 21H
code ends
end start
