Minimum DXF file requirements for Microstation to open it?

I am trying to determine the minimum requirements for a DXF file that can be opened by Microstation.

I have some very simple DXF samples from the internet that I can view in freeware viewers.  When I try to open with Microstation it says Unable to open design file.  If I save a Microstation DGN with a single line in it to DXF format, I get a DXF file with 32,000 lines.  Does anyone have a very simple DXF that Microstation will open I could use as a starting point or some advice on what Microstation requires in a DXF?

TIA,

Tim