Hi

This is just to share with you my own experience. I have done experiments with the AT89C51, AT89C52, AT89S52 and then moved to P89V51RD2

From a simple convenience perspective, here are the advantages P89V51RD2 that I have experienced
- No need of any external programmer
- Just connect your serial port to the P89V51RD2 directly on target board.
- Install "Flash Magic" software on your PC and you are good to go !!
- No painful moving of the chip from programmer to target board etc.
- The 89V51RD2 has onboard 1K RAM and 64K Flash ROM so that is good too
- 89V51RD2 is twice the cost of the AT89C51 so if you are not thinking production, its worth it.