计算机汇编语言小程序求助

AX=00EFh
BX=002Fh
CX=0033h
DX=0000h

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CSEG SEGMENT
ASSUME CS:CSEG, DS: CSEG, SS:CSEG
ORG 100H
BEGIN: MOV AX,3FH
MOV BX,2FH
MOV CX,04H
MOV DX,0FH
SUB AX,BX
JBE L20
NOT AX
L20: AND AX,0FFH
ADD CX,BX
XOR DX,DX
int 3
CSEG ENDS
END BEGIN