I have a project 320 with cn10 so its the same gcode with you.
First of all i need to realise what exactly you want to do.
1. If you want to do an ellipse you use G108 or G109 depending from the direction you want it to have.
with G108 you can make an ellipse clockwise and
with G109 -""- anticlockwise.
When you are starting your machine inside function 1. "PROGRAMMING " create a test program.
Push the right arrow KEY and then the F8 KEY(HELP).
This will take you to a help table called "INDEX OF THE ISO CODES IN NUMERICAL ORDER", and G108 and G109 are on the 2nd page with their way of syntax.
Now try this example. write this code:
G172 X50 Y50 Z2 T25/1 S17 E1
G101 X100 Y100 F5
G108 I200 J100 R360 Q0 F5
G101 X50 Y150
This will show you a circle from x100,y100 to x100,y100
Now in G108, try to change R.
360 is 360 degrees, put it 270, then 180, then 90, then 45 and again 360.
It does 3quaters in 270, 2quaters in 180, 1 in 90, and a half of one 45deg in 45.
Now you can see why i put the two G101, only to can watch better where it starts and ands the ellipse.
Now play with Q.
Put in Q the price 1, then the price 2, 3, 4, 5, as many as you want but put also the price 500 or 900.
every ellipce has an eccentricity wich is the distance between its two centers (shearch in google about the schema of an ellipse if you need it).
Q is this distance, thats why at the begining wich was 0 the two centers where one so the ellipce was a circle and when you increase this distance to 1mm, 2mm e.t.c.it looks more like ellipse.
but when you put a very big price like 500 or 900 it is like a straight line.
Hope to help you