I've been studing a little , and I did something good, for my application.

LAR1     AR2 L        P##Buffer TAR1 +D LAR1 TAR1     #offset

Just like Fritz said, if my IDB is larger than 4Kb. I can use this
code to find the offset of my FB multi instancied.

But my DB is not larger than that, so Im using that
more simple.

I know that AR2 have a pointer for the first octet of my IDB, so
for my FB Multi Instancied.

LAR1   AR2          //save the pointer of AR2 in AR1       L      #Buffer      //load the pointer of my Buffer +AR1                //Address + offset TAR1   #addrBuffer  //addrBuffer have the absolut address of my buffer

Thanks very much André and Fritz, you guys helped me a lot a understand that,
the pointers, AR1 and AR2 registers.

now i can work very well with Multi-Instances.
Merci beaucoup
au revoir.

Cheers
Pedro RUIZ