Erik,

thank you for the exact code and explanations.

Unfortunately this will not resolve my issues.

We have eleven different possible hardware members on this RS485 network and up to 9 at a time (usually 6). 9 of these devices use the AT89C51RB2 chip, 2 use a uPSD chip. The application software of all eleven devices is hosted by the master device. If we substitute the Atmel by the NXP for production reason, the application area code needs to be identical and compatible with the current code. These are devices that run since years and I can not program dedicated NXP or Atmel application code because of spare parts incompatibility. The only thing I can change is the boot loader, since it is not hosted by the master and will not be downloaded.

In addition, I am not going to rewrite the software of these 9 devices and tweak ISR calls just because NXP can't have a boot loader that runs independent of the application software. It is too much work for testing and re-certifying all the devices.
Again, the Atmel solution is easy to understand and the Atmel data sheet provides useful information for the implementation. There is no need to tweak the ISR calls or anything else.

I have my solution, thanks to Jan. He said that the P89V51Rx2 series is the same like the SST89E516RD. I looked to the data sheet and I found exactly the information I need. I already made some little code to test erase, read, write and jumping between application and boot loader code. So far it looks very promising.

I would like to thank here to all that gave me their valuable inputs.
Stefan Lu