I need help about NXP MCU,P89C662HBA,which can start user's code but can't start ISP masked-ROM boot loader code.But why?even though I push PSEN pin to GND. when I want to down load my code,I have to push PSEN pin to GND in order to start ISP masked-ROM boot loader code,after a few sucess times,Now,fail to start boot loader code ,so I can't down load my code using this way. what's wrong my Behavior? I need Help.
I Push EA to VCC and PSEN to GND directly,Push ALE,P2.6,P2.7 to VCC through pull-up resistor,But I still can't down load my code