You must configure the digitizer so a movement on the digitizing tablet can be recorded directly into an existing drawing file as you digitize.
To configure the digitizer
When you complete the configuration, two new options appear on the status bar at the bottom of the AutoCAD Map 3D window. Tablet and FLOAT let you toggle the two modes.
Use the Options dialog box to disable the mouse while you are digitizing.
When you complete digitizing, return to the Options dialog box and select the Digitizer And Mouse option to use both input devices.