General Description: When I run Incremental or Modular Design on a Spartan-3 device that uses 3-state logic in the modules or Area Groups, the following error occurs in MAP:
"ERROR:MapLib:653 - Mapping operation involving: BUFT symbol "x"... BUFE symbol "y"... etc. cannot be completed because it crosses a Incremental Design Area Group boundary. The original logic will remain intact."
Due to the lack of TBUFs in the Spartan-3 architecture, XST and MAP transform 3-state logic to LUTs in a typical design. In Modular and Incremental Design, there are different rules that do not allow XST or MAP to completely resolve 3-state logic because of incremental or modular boundaries. For Spartan-3, Modular and Incremental designs must have all 3-state logic driving the same signal at the same level of hierarchy.