Can I cancel a movement command in progress?

If I instruct the arm to move to a position using a GCode command, can I cancel that command before it has completed executing it?

Also I cannot get the wrist to move at all via the serial port GCode command. If I send anything like:
G2202 N3 V90\n

I just get an E21 error.

You should set the speed if you use the firmware version is 4.x.x