I have written a bootloader program to sit on the P89C664 processor. The problem is that if I then try to user a timer interrupt to fresh an external watchdog then the program falls over. I suspect, but cannot prove that the first time that the program moves to the code contained in the bootloader section of the code space that the interrupt cause incorrect return on exit. The only proof I have is that the boot vector and status byte of the chip are set to the bootloaders entry requirements and have not been reset. The easiest method would be to use the onboard watchdog, burt this is automatically disabled during flash operations. Given that the erase cycle is measuerd in seconds I don't like that idea. Does anybody know of a way to prevent this problem??