In the latest version of the manual, it explains this on Pages 3-4 and 3-5.
Look under the section "Changing the screen rotation" for Boot Screen. Whatever the Boot Screen is set to (the screen config with the * next to it), will be what the D100 starts up looking like.
I don't have a hobbs in my aeroplane, so I've set my boot screen to be 1/3 Time, so it's easy to make note of startup time.
The latest manual is here: http://www.dynonavionics.com/downloads/User_Manuals/EFIS-D100%20Pilot%27s%20User%20Guide.pdf