Checksum calculation

[suhas_5678]

Hi,
I am working on a programming tool for the P89V51RD2 controller as my final year project. Have gone through the data sheets completely and have successfully brought the controller into ISP mode but don't know how to proceed further. How do I calculate the check sum required for sending the command/data function? The controller echos back anything I send it regardless of whether I send ASCII or HEX equivalent of the examples given in the data sheets, it does not send 'X' as mentioned in the data sheets.

Please help.

With regards,
Suhas

[sanketbarot]

I am not able to understand u, can you be more specific