PROMGen Files

This section describes the PROMGen input and output files.

Input Files

The input to PROMGEN consists of BIT files - one or more bitstream files. BIT files contain configuration data for an FPGA design.

Output Files

Output from PROMGEN consists of the following files.

• PROM files - The file or files containing the PROM configuration information. Depending on the PROM file format your PROM programmer uses, you can output a TEK, MCS, or EXO file. If you are using a microprocessor to configure your devices, you can output a HEX file, which contains a hexadecimal representation of the bitstream.
  
  
• PRM file - The PRM file is a PROM image file. It contains a memory map of the output PROM file. The file has a .prm extension.
  
  

Bit Swapping in PROM Files

PROMGen produces a PROM file in which the bits within a byte are swapped compared to the bits in the input BIT file. Bit swapping (also called “bit mirroring”) reverses the bits within each byte, as shown in the following figure.

Figure 14.2 Bit Swapping

In a bitstream contained in a BIT file, the Least Significant Bit (LSB) is always on the left side of a byte. But when a PROM programmer or a microprocessor reads a data byte, it identifies the LSB on the right side of the byte. In order for the PROM programmer or microprocessor to read the bitstream correctly, the bits in each byte must first be swapped so they are read in the correct order.

In this release of the Xilinx Development System, the bits are swapped for all of the PROM formats: MCS, EXO, and TEK. For a HEX file output, bit swapping is on by default, but it can be turned off by entering a -b PROMGen option that is available only for HEX file format.