has anybody tried the programmer given in the AT89c51 programming datasheet??

I have not seen any programmer in the datasheet of AT89C51, rather it contains programming algorithm. Do you mean that programming algorithm?

As far as 13V and 6.5V are concerned, some 89C51 require 5V as programming voltage, while some 89C51 chips require 12.5V. AT89C55WD requires 6.5V as VCC for programming.

The programmer identifies the correct programming voltage (5 or 12) by reading the signature bytes.

For more info on signature bytes, consult the data sheet.

Regards

IA