Aaaaah there would be no excitement in electronics if you'd never sail away from your home lake...



Maybe yes, maybe not. There are 3 factors in "loosing" the P89V51RD2 (i.e. corrupting the bootloader in bootFLASH - this is not inadvertent, a parallel programmer (if available :-( ) can be used to reprogram the boot sector):

• as you said, accidental overwriting of ISP area by the application. This sounds reasonable, but it is not easy to accomplish at all, at least not if one is not aware of the exact procedures of FLASH writing, which are hidden from the user by the IAP interface.
  
• an unfortunate flaw in the ISP protocol, due to which the SoftICE mode is set when programmed using FlashMagic and - by (not too uncommon) mistake - the P89C51RD2 is chosen. In this case the chip stops responing to FlashMagic, but remedy exists (see "unsoftice" on my webpage).
  
• Circuitry - the classic example. What is the power supply characteristic and what is the RESET circuit? RC, isn't it? Although the datasheet claims some POR and BOD, the explanation - ehm - leaves a lot behind - and the SST's datasheet is not any clearer in this regard (I'd guess they simply sc****d it up and it does not work properly - as in so many other mcus...).
  

And, of course, the fourth - completely damaged chip, for a zillion of reasons.


The only thinkg I dare to guarantee is that there will be a sunset tonight... :-)

However, if I managed to use IAP (consider my innate stupidity), I believe it is not so complicated - one just needs to read what has been written here and in the datasheet, very very carefully.... But wait, oh, isn't this the case of so many troubles? :-)

Jan Waclawek