An ASCII text file (with the extension .tdf) written in the Altera^® Hardware Description Language (AHDL).

A TDF can contain any combination of Boolean equations, truth tables, state machines, and group operations. TDFs can also be parameterized.

You can easily incorporate Altera-provided primitives and both Altera-provided megafunctions and user-defined megafunctions and macrofunctions, including library of parameterized modules (LPM) functions, into a TDF. You can use a mega- or macrofunction by creating a Function Prototype and inserting an instance of the function into the TDF. You can also use this method to incorporate TDF logic in another TDF. You can also automatically generate a default AHDL Include File (.inc) that contains a Function Prototype for any design file by choosing Create/Update > Create AHDL Include Files for Current File (File menu).

TDFs can be incorporated into both top-level entities and lower-level entities in a project. The Quartus^® II software automatically creates a Block Symbol File (.bsf) that represents any design file when you choose Create/Update > Create Symbol Files for Current File (File menu). This symbol and the logic it represents can be incorporated into a Block Design File (.bdf).

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