Auto-Cad - Isometric Circles 

Forming Isometric Circles Ellipse In CAD
Draw Isometric Circles - STEPS
Click Tools menu for Drafting Settings.
In the Drafting Settings dialog box, Snap and Grid tab, under Snap Type, select Isometric Snap.
Click OK.
Click Drafting tab then Draw panel then Ellipse drop-down.
Enter i -Isocircle-.
Specify the center of the isocircle.
Specify the radius or diameter of the isocircle.