MSP430F2619: How to update only 1-byte data in the information memory (SegA) ?

Part Number:MSP430F2619

Dear All,

I would like to know how to update only 1-byte data in the information memory (SegA) of MSP430F2619?

For example:

Seg A (0x1000)          :  01 02 03 04 05 06 .....

    => update 3th byte to 0x77

                                    :  01 02 77 04 05 06 .....     

Thank you.

Sunglin.