The 'V51RD2 is one order of magnitude "smarter" than the plain 'C52. Most notably, it is able to reprogram itself, and has a builtin program called bootloader, which is able to receive data via UART and "burn" it to its own FLASH.

Your "programmer" is using this feature, called ISP (for In-Situ Programming) - and I like to add, UART-ISP.

The 'C52 is much more down to the roots design, being only a standard "vanilla" 8052 core plus a FLASH. The core cannot "burn" the FLASH and the only way to program it is a so called parallel device programmer; but that's an order of magnitude more complex than your "programmer" and usually costs $$$s. The 'V51RD2 can be programmed in a parallel programmer, too; but the programming algorithm is different from that of 'C52.

Also, please note, that the whole AT89C5x family is now obsolete (or, in Atmel's lingo, "mature"), and are being replaced by the AT89S5x family. The latter, besides parallel programming, does implement ISP, but a different form of it, more like SPI (data & clock).

Please note, that Atmel does produce a similar chip than the P89V51RD2, called AT89C51RD2/AT89C51ED2, but I suspect you have chosen the plain 'C52 because of its low cost, which the RD2s (of any manufacturer - Winbond makes them too, as well as SST), being more complex and sophisticated, have not.

JW

PS. You might want to check out the "burning '51s" FAQ...