BitGen Files

The input files that BitGen requires and the output files that BitGen generates are described below.

Input Files

Input to BitGen consists of the following files.

• NCD file - a physical description of the design mapped, placed and routed in the target device. The NCD file must be fully routed.
  
  
• PCF - an optional user-modifiable ASCII Physical Constraints File. If you specify a PCF file on the BitGen command line,
  
  BitGen uses this file to determine which nets in the design are critical for tiedown (see the “-t (Tie Unused Interconnect)” section).
  
  

Output Files

Output from BitGen consists of the following files.

• BIT file - a binary file with a .bit extension. The BIT file contains all of the configuration information from the NCD file defining the internal logic and interconnections of the FPGA, plus device-specific information from other files associated with the target device. The binary data in the BIT file can then be downloaded into the FPGA's memory cells or it can be used to create a PROM file (see the “PROMGen” chapter).
  
  
• RBT file - an optional “rawbits” file with an .rbt extension. The rawbits file consists of ASCII ones and zeros representing the data in the bitstream file. If you enter a -b option on the BitGen command line. an RBT file is produced in addition to the binary BIT file (see the “-b (Create Rawbits File)” section).
  
  
• LL file - an optional ASCII logic allocation file with an .ll extension. The logic allocation file indicates the bitstream position of latches, flip-flops, and IOB inputs and outputs. An LL file is produced if you enter a -l option on the BitGen command line (see the “-l (Create a Logic Allocation File)” section).
  
  
• MSK file - an optional mask file with an .msk extension. This file is used to compare relevant bit locations for executing a readback of configuration data contained in an operating FPGA. A MSK file is produced if you enter a -m option on the BitGen command line (see the “-m (Generate a Mask File)” section).
  
  
• BGN file - a report file containing information about the BitGen run.
  
  
• DRC file - a Design Rule Check (DRC) file for the design. A DRC runs and the DRC file is produced unless you enter a -d option on the BitGen command line (see the “-d (Do Not Run DRC)” section).