org 0000h
AJMP MAIN
ORG 001BH
AJMP SERVE
MAIN:MOV TMOD,#10H
MOV 20H,#0AH
CLR A
MOV 30H,A
MOV 31H,A
MOV 32H,A
SETB ET1
SETB EA
MOV TH1,#3CH
MOV TL1,#0B0H
SETB TR1
SJMP $
SERVE:PUSH PSW
PUSH ACC
MOV TH1,#3CH
MOV TL1,#0B0H
DJNZ 20H,RETUNT
MOV 20H,#0AH
MOV A,#01H
ADD A,32H
DA A
MOV 32H,A
CJNE A,#60H,RETUNT
MOV 32H,#00H
MOV A,#01H
ADD A,31H
DA A
MOV 31H,A
CJNE A,#60H,RETUNT
MOV 31H,#00H
MOV A,01H
ADD A,30H
DA A
MOV 30H,A
CJNE A,#24H,RETUNT
MOV 30H,#00H
RETUNT:POP ACC
POP PSW
RET

end

搞定了，原來是書上印漏了點東西。
MOV A,01H
這條應改為MOV A,#01H
RET改為RETI