Hi Erik,

but nevertheless its still possible to change the boot vector byte to a wrong location.

Then it reacts like the boot loader was erased.

You can try to get the boot loader code and burn it into an external EPROM. Then reprogram the boot vector byte to FCh. I hope this works.


In opposition the Atmel T89C51CC01, if PSEN was hold low during reset, ignore the boot vector byte and jump always to the boot loader at F800h. Also this boot loader can never be erased in the serial programming mode (at 5V).

So only the Atmel seems to be proofed to return from every wrong programming state without removing it from the pcb and insert it in the parallel programmer.


Peter