Variables in IDATA space are naturally accessed indirectly, so IDATA is the natural place to put variables that you plan to access through pointers. (You could just as well put indirectly accessed variables in the DATA space, except that you will probably want to conserve it for directly addressed variables due to its limited size.)

For that reason always declare indirtect addressed variables as IDATA, if they fit in DATA space anyhow, they will (at least with Keil) go there anyhow. If, however, you declare them DATA (I have space enough - famous last words) you will have to hunt up all indirectly addressed DATA and change them to IDATA when you run out of DATA space - been there, done that.

Erik