第2个回答 2013-10-29
ORG 0000H
LJMP MAIN
ORG 000BH
LJMP PGT0
ORG 0030H
MAIN:MOV R2,#100
MOV R3,#180
MOV TMOD,#1
MOV TL0,#LOW(65536-10000)
MOV TH0,#HIGH(65536-10000)
SETB TR0
SETB ET0
SETB EA
AJMP $
PGT0:MOV TL0,#LOW(65536-10000)
MOV TH0,#HIGH(65536-10000)
DJNZ R2,X
MOV R2,#100
MOV A,R3
CJNE A,#30,Y
CLR P2.7
Y:DJNZ R3,X
CLR EA
SETB P2.7
X:RETI
蜂鸣器接P2.7,负逻辑驱动