Okay, suppose your drive is on A:

You can turn the motor on and light the select LED with this command in DEBUG:

o 3F2 1C

The same for drive B:

o 3F2 2D

The following commands

o 3F5 0
i 3f4

Should get a result of D0. Follow this with

i 3f5

you should get 80.

Your mileage may vary, depending on the controller.